We re-write the interrupts and timer section to align the
interrupts and timer table. We also add more fine grained
requirements for AIA.

Signed-off-by: Anup Patel <anup.patel@...>
---
Makefile | 4 +-
riscv-platform-spec.adoc | 323 ++++++++++++++++++++++-----------------
riscv-platform-spec.yml | 8 +
3 files changed, 193 insertions(+), 142 deletions(-)
create mode 100644 riscv-platform-spec.yml

diff --git a/Makefile b/Makefile
index 48e8fe9..ff8fbf6 100644
--- a/Makefile
+++ b/Makefile
@@ -22,8 +22,8 @@ $(PLATFORM_SPEC).md: $(PLATFORM_SPEC).xml
$(PLATFORM_SPEC).xml: $(PLATFORM_SPEC).adoc
$(ASCIIDOCTOR) -d book -b docbook $<

-$(PLATFORM_SPEC).pdf: $(PLATFORM_SPEC).adoc $(IMAGES)
- $(ASCIIDOCTOR) -d book -r asciidoctor-pdf -b pdf $<
+$(PLATFORM_SPEC).pdf: $(PLATFORM_SPEC).adoc $(IMAGES) $(PLATFORM_SPEC).yml
+ $(ASCIIDOCTOR) -d book -r asciidoctor-pdf -a pdf-style=$(PLATFORM_SPEC).yml -b pdf $<

$(PLATFORM_SPEC).html: $(PLATFORM_SPEC).adoc $(IMAGES)
$(ASCIIDOCTOR) -d book -b html $<
diff --git a/riscv-platform-spec.adoc b/riscv-platform-spec.adoc
index cffb71c..3994ef3 100644
--- a/riscv-platform-spec.adoc
+++ b/riscv-platform-spec.adoc
@@ -13,6 +13,7 @@
:doctype: book
:sectnums:
:sectnumlevels: 5
+:xrefstyle: short
:toc: macro
:toclevels: 5

@@ -235,114 +236,173 @@ each must be 1
The default should allow code that's sensitive to these requirements to be
debugged.

-==== Interrupt Controller, Software Interrupt, and Timer Requirements
-In the following requirements,
-https://github.com/riscv/riscv-aia[*AIA*] refers to the Advanced Interrupt Architecture, https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[*ACLINT*]
-refers to the Advanced *CLINT*. AIA comprises two separate components: `IMSICs` and `APLICs`.
-If supported, there is an `IMSIC` device associated with each hart.
-If supported, *APLIC* devices are global to all harts, and there may be one or
-multiple in a system. *ACLINT* comprises three separate components: `MTIMER` for
-Timer support, and `MSWI` and `SSWI` for Machine-level and Supervisor-level
-Software Interrupt (IPI) support. +
-https://github.com/riscv/riscv-plic-spec/blob/master/riscv-plic.adoc[*PLIC*]
-refers to the legacy Platform-Level Interrupt Controller that provides
-facilities to route external interrupts to a hart context with a given privilege
-mode. The number of non-local interrupt sources supported by PLIC and how does
-each of them connect to the hart context is PLIC core implementation-specific. +
-*CLINT* is a legacy Core-Local Interrupt Controller that is a compatible subset of
-ACLINT which provides facilities to trigger Software (IPI) and Timer interrupts to
-hart.
+==== Interrupts and Timer
+
+===== Timer support
+
+* One or more ACLINT MTIMER devices are required for the OS-A platform
+* All MTIME counters must be 64-bit counters with a 10ns resolution (i.e.
+ an increment by 1 represents 10 ns).
+* The MTIME update frequency (i.e. hardware clock) must be between 10 MHz
+ and 100 MHz, and updates must be strictly monotonic.
+* Platforms must provide a way to discover MTIME resolution using appropriate
+ hardware discovery mechanism:
+** Platforms that use DT for hardware discovery are required to advertise the
+ timebase to the operating systems via the `timebase-frequency` property of
+ the "/cpus" node
+footnote:[https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/riscv/cpus.yaml].
+
+[sidebar]
+--
+[underline]*_Implementation Note_*

-.The following table summarizes what features are supported for four classes of OS/A platforms.
-[width="100%",cols="^,^,^,^,^,^,^,^,^,^,^,^,^"]
-|=======
-.2+|*OS-A Platform* 3+|*MSIs* 3+|*Wired Interrupts* 3+|*IPIs* 3+|*Timer*
-|M-level|S-level|VS-level|M-level|S-level|VS-level|M-level|S-level|VS-level|M-level|S-level|VS-level
-|Existing|NA|NA|NA|PLIC|PLIC|PLIC +
-_(Trap and emulate)_|MSWI +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|SBI Timer +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|SBI Timer +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]
-|Only Wired IRQs|NA|NA|NA|APLIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|MSWI +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-SSWI +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
-|MSIs and Wired IRQs|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
-|MSIs, Virtual MSIs and Wired IRQs|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC VS-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC VS-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
-|=======
-
-* For Timer support, one or more ACLINT MTIMER devices are Required for OS-A platform.
-One MTIMER may be used for all harts, or multiple MTIMERs may be used with
-multiple topological groups of harts. The base address of MTIMER memory map registers
-is platform implementation-specific, however, the format of MTIMER operation parameters
-(`mtime` and `mtimecmp` registers) must be compliant with
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc#21-register-map[ACLINT MTIMER Register Map]
-
-* For Interrupt Controller and Software Interrupt support, one of the following three
-choices below is Required
- ** PLIC plus one or more ACLINT MSWI devices - DEPRECATED
- *** One MSWI may be used for all harts, or multiple MSWIs may be used with
-multiple topological groups of harts
- *** Only wired interrupts and M-mode IPIs are supported
- *** Virtualization is not supported
- *** This compatibly supports legacy PLIC + CLINT designs
- ** One or more AIA APLIC devices plus one or more pairs of ACLINT MSWI and ACLINT SSWI devices
- *** One MSWI/SSWI pair may be used for all harts, or multiple MSWI/SSWI
-pairs may be used with multiple topological groups of harts
- *** Only wired interrupts are supported
- *** Both M-mode and S-mode IPIs are supported
- *** Virtualization is not supported
- ** Zero, one, or more AIA APLIC devices plus per-hart AIA IMSIC devices
- *** Both wired and MSI external interrupts are supported
- *** Both M-mode and S-mode IPIs are supported via IMSICs
- *** Virtualization is supported
- *** Zero APLICs if there are no wired interrupts and only MSIs
+For example, if `timebase-frequency` is 100 MHz and the MTIME update
+frequency (i.e. hardware clock) is 25 MHz then the MTIME counter would
+increment by 4 upon every hardware clock tick.
+--
+
+===== Interrupts support
+
+The OS/A platorms can comply with one of the following four categories for
+interrupts support:
+
+* *Legacy IRQs - DEPRECATED*
+** One or more PLIC devices to support wired interrupts
+** One or more ACLINT MSWI devices to support M-mode software interrupts
+** Software interrupts for S-mode and VS-mode supported using the
+ SBI IPI extension
+** Compatibile with legacy platforms having PLIC plus CLINT devices
+** MSI external interrupts not supported
+** MSI virtualization is not supported
+* *Only Wired IRQs*
+** One or more AIA APLIC devices to support wired interrupts
+** One or more ACLINT MSWI devices to support M-mode software interrupts
+** One or more ACLINT SSWI devices to support HS-mode software interrupts
+** Software interrupts for VS-mode supported using the SBI IPI extension
+** MSI external interrupts not supported
+** MSI virtualization is not supported
+* *MSIs and Wired IRQs*
+** AIA local interrupt CSRs must be supported by each hart
+*** `mvien` and `mvip` CSRs must be implemented
+*** `hvien` and `hvip` CSRs must be implemented if H-extension is implemented
+*** `siselect` CSR must support holding a 9-bit value
+*** `vsiselect` CSR must support holding a 9-bit value if H-extension
+ is implemented
+** Per-hart AIA IMSIC devices must support MSIs for M-mode and HS-mode
+*** IPRIOLEN = 6 to 8
+*** MIFMAX = SIFMAX = 63 to 255
+*** Must support at least 63 distinct interrupt identities
+*** Must implement `seteipnum_le` memory-mapped register
+** One, or more AIA APLIC devices to support wired interrupts
+*** EIID and IID fields must be 6 to 8 bits wide matching the number of
+ interrrupt identities supported by AIA IMSIC
+** Software interrupts for M-mode and HS-mode supported using AIA IMSIC devices
+** Software interrupts for VS-mode supported using the SBI IPI extension
+** MSI virtualization is not supported
+* *MSIs, Virtual MSIs, and Wired IRQs*
+** The H-extension must be implemeted by each hart to support virtual MSIs
+*** GEILEN must be 1 or more
+** AIA local interrupt CSRs must be supported by each hart
+*** `mvien` and `mvip` CSRs must be implemented
+*** `hvien` and `hvip` CSRs must be implemented
+*** `siselect` CSR must support holding a 9-bit value
+*** `vsiselect` CSR must support holding a 9-bit value
+** Per-hart AIA IMSIC devices to support MSIs for M-mode, HS-mode and VS-mode
+*** IPRIOLEN = 6 to 8
+*** MIFMAX = SIFMAX = GIFMAX = 63 to 255
+*** Must support at least 63 distinct interrupt identities
+*** Must implement `seteipnum_le` memory-mapped register
+*** Must implement at least 1 guest interrupt file
+** One, or more AIA APLIC devices to support wired interrupts
+*** EIID and IID fields must be 6 to 8 bits wide matching the number of
+ interrrupt identities supported by AIA IMSIC
+** Software interrupts for M-mode, HS-mode and VS-mode supported using
+ AIA IMSIC devices
+** MSI virtualization is supported
+
+===== Summary
+
+The <<table_interrutps_and_timer_osa_platforms>> below summarizes the four
+categories of timer and interrupt support allowed in a OS/A platorm.
+
+[#table_interrutps_and_timer_osa_platforms]
+.Interrupts and Timer support in OS/A platforms
+[stripes="none", width="100%", cols="^2s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s"]
+|===
+.2+|+++<font size=".8em">OS-A Platform</font>+++
+3+|+++<font size=".8em">MSIs</font>+++
+3+|+++<font size=".8em">Wired Interrupts</font>+++
+3+|+++<font size=".8em">Software Interrupts</font>+++
+3+|+++<font size=".8em">Timer</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+
+|+++<font size=".8em">Legacy IRQs</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">PLIC</font>+++ ^<<spec_plic>>^
+|+++<font size=".6em">PLIC</font>+++ ^<<spec_plic>>^
+|+++<font size=".6em">PLIC (emulate)</font>+++ ^<<spec_plic>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MSWI</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI Timer</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI Timer</font></color>+++ ^<<spec_sbi>>^
+
+|+++<font size=".8em">Only Wired IRQs</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MSWI</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#6aa84f"><font size=".6em">SSWI</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+
+|+++<font size=".8em">MSIs and Wired IRQs</font>+++
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+
+|+++<font size=".8em">MSIs, Virtual MSIs and Wired IRQs</font>+++
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|===

==== System Peripherals
* UART/Serial Console
@@ -359,27 +419,6 @@ of the following:
** UART 16550 - _REQUIRED_
** UART 8250 - _DEPRECATED_

-* Clock and Timers
-** Platforms are required to provide an at least 10ns resolution 64-bit counter
-with strictly monotonic updates.
-** The hardware clock that drives the counter is required to operate at a minimum
-frequency of 10MHz.
-** Platforms that use DT for hardware discovery are required to advertise the
-timebase to the operating systems via the `timebase-frequency` property of the
-"/cpus" node
-footnote:[https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/riscv/cpus.yaml].
-
-[sidebar]
---
-[underline]*_Implementation Note_*
-
-For a counter with 10ns resolution the `timebase-frequency` value would be 100000000
-(100 MHz) which would also be the minimum possible value for `timebase-frequency`.
-From the software perspective a unit increment of the mtime value would correspond
-to a 10ns interval. However the hardware clock driving the counter could operate at a
-lower frequency, thereby incrementing the mtime value by more than one unit per
-clock tick.
---
==== Boot Process
- The base specification defines the interface between the firmware and the
operating system suitable for the RISC-V platforms with rich operating
@@ -449,6 +488,8 @@ base with the additional requirements as below.
The platforms which conform to server extension are required to implement +

* RV64 support
+* The `time` CSR must be implemented in hardware
+* The Sstc extension <<spec_priv_sstc>> must be implemented
* RISC-V ISA H-extension with following additional requirements:
** VMID support
** Upon load/store/AMO exceptions taken into HS-mode, the `htinst` CSR must
@@ -489,7 +530,20 @@ above.
respect to all harts connected to the DM
* Rationale: Debuggers must be able to view memory coherently

-==== Interrupt Controller
+==== Interrupts and Timer
+
+The OS-A server platform must comply with "MSIs, Virtual MSIs and Wired IRQs"
+category of interrupts and timer support defined in the base with following
+additional requirements:
+
+* The H-extension implemented by each hart must support GEILEN = 3 or more
+* Per-hart AIA IMSIC devices
+** Must implement at least 3 guest interrupt files
+** Must support at least 255 distinct interrupt identities
+** IPRIOLEN = 8
+** MIFMAX = SIFMAX = GIFMAX = 255
+* EIID and IID fields of AIA APLIC devices must be at least 8 bits wide
+ matching the number of interrrupt identities supported by AIA IMSIC

==== Boot and Runtime Requirements
===== Firmware
@@ -659,12 +713,6 @@ implemented but it can return EFI_UNSUPPORTED.
|===

==== System Peripherals
-===== Clock and Timers
-** Platforms are required to implement the time CSR.
-** Platforms are required to implement the Sstc extension <<spec_priv_sstc>>.
-** Platforms are required to delegate the supervisor timer interrupt to 'S'
-mode. If the 'H' extension is implemented then the platforms are required to
-delegate the virtual supervisor timer interrupt to 'VS' mode.

===== Watchdog Timers
Implementation of a two-stage watchdog timer, as defined in the WatchDog Timer
@@ -897,11 +945,6 @@ in the physical RV processor. +
* Logging and/or reporting of errors can be masked. +
* PCIe AER capability is required. +

-==== Interrupt Controller, Software Interrupt, and Timer Requirements
- * For Timer support, ACLINT MTIMER devices is/are Required
- * For Interrupt Controller and Software Interrupt support, the following one choice is Required
- - Zero, one, or more AIA APLIC devices plus per-hart AIA IMSIC devices
-
// M Platform
== M Platform

diff --git a/riscv-platform-spec.yml b/riscv-platform-spec.yml
new file mode 100644
index 0000000..ce00e22
--- /dev/null
+++ b/riscv-platform-spec.yml
@@ -0,0 +1,8 @@
+extends: default
+image:
+ align: center
+caption:
+ align: center
+table:
+ caption:
+ side: bottom
--
2.25.1

On 8/6/21 8:19 AM, Anup Patel wrote:

We re-write the interrupts and timer section to align the
interrupts and timer table. We also add more fine grained
requirements for AIA.
Signed-off-by: Anup Patel <anup.patel@...>
---
Makefile | 4 +-
riscv-platform-spec.adoc | 323 ++++++++++++++++++++++-----------------
riscv-platform-spec.yml | 8 +
3 files changed, 193 insertions(+), 142 deletions(-)
create mode 100644 riscv-platform-spec.yml
diff --git a/Makefile b/Makefile
index 48e8fe9..ff8fbf6 100644
--- a/Makefile
+++ b/Makefile
@@ -22,8 +22,8 @@ $(PLATFORM_SPEC).md: $(PLATFORM_SPEC).xml
$(PLATFORM_SPEC).xml: $(PLATFORM_SPEC).adoc
$(ASCIIDOCTOR) -d book -b docbook $<
-$(PLATFORM_SPEC).pdf: $(PLATFORM_SPEC).adoc $(IMAGES)
- $(ASCIIDOCTOR) -d book -r asciidoctor-pdf -b pdf $<
+$(PLATFORM_SPEC).pdf: $(PLATFORM_SPEC).adoc $(IMAGES) $(PLATFORM_SPEC).yml
+ $(ASCIIDOCTOR) -d book -r asciidoctor-pdf -a pdf-style=$(PLATFORM_SPEC).yml -b pdf $<
$(PLATFORM_SPEC).html: $(PLATFORM_SPEC).adoc $(IMAGES)
$(ASCIIDOCTOR) -d book -b html $<
diff --git a/riscv-platform-spec.adoc b/riscv-platform-spec.adoc
index cffb71c..3994ef3 100644
--- a/riscv-platform-spec.adoc
+++ b/riscv-platform-spec.adoc
@@ -13,6 +13,7 @@
:doctype: book
:sectnums:
:sectnumlevels: 5
+:xrefstyle: short
:toc: macro
:toclevels: 5
@@ -235,114 +236,173 @@ each must be 1
The default should allow code that's sensitive to these requirements to be
debugged.
-==== Interrupt Controller, Software Interrupt, and Timer Requirements
-In the following requirements,
-https://github.com/riscv/riscv-aia[*AIA*] refers to the Advanced Interrupt Architecture, https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[*ACLINT*]
-refers to the Advanced *CLINT*. AIA comprises two separate components: `IMSICs` and `APLICs`.
-If supported, there is an `IMSIC` device associated with each hart.
-If supported, *APLIC* devices are global to all harts, and there may be one or
-multiple in a system. *ACLINT* comprises three separate components: `MTIMER` for
-Timer support, and `MSWI` and `SSWI` for Machine-level and Supervisor-level
-Software Interrupt (IPI) support. +
-https://github.com/riscv/riscv-plic-spec/blob/master/riscv-plic.adoc[*PLIC*]
-refers to the legacy Platform-Level Interrupt Controller that provides
-facilities to route external interrupts to a hart context with a given privilege
-mode. The number of non-local interrupt sources supported by PLIC and how does
-each of them connect to the hart context is PLIC core implementation-specific. +
-*CLINT* is a legacy Core-Local Interrupt Controller that is a compatible subset of
-ACLINT which provides facilities to trigger Software (IPI) and Timer interrupts to
-hart.
+==== Interrupts and Timer
+
+===== Timer support
+
+* One or more ACLINT MTIMER devices are required for the OS-A platform
+* All MTIME counters must be 64-bit counters with a 10ns resolution (i.e.
+ an increment by 1 represents 10 ns).
+* The MTIME update frequency (i.e. hardware clock) must be between 10 MHz
+ and 100 MHz, and updates must be strictly monotonic.
+* Platforms must provide a way to discover MTIME resolution using appropriate
+ hardware discovery mechanism:
+** Platforms that use DT for hardware discovery are required to advertise the
+ timebase to the operating systems via the `timebase-frequency` property of
+ the "/cpus" node
+footnote:[https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/riscv/cpus.yaml].
+
+[sidebar]
+--
+[underline]*_Implementation Note_*
-.The following table summarizes what features are supported for four classes of OS/A platforms.
-[width="100%",cols="^,^,^,^,^,^,^,^,^,^,^,^,^"]
-|=======
-.2+|*OS-A Platform* 3+|*MSIs* 3+|*Wired Interrupts* 3+|*IPIs* 3+|*Timer*
-|M-level|S-level|VS-level|M-level|S-level|VS-level|M-level|S-level|VS-level|M-level|S-level|VS-level
-|Existing|NA|NA|NA|PLIC|PLIC|PLIC +
-_(Trap and emulate)_|MSWI +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|SBI Timer +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|SBI Timer +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]
-|Only Wired IRQs|NA|NA|NA|APLIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|MSWI +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-SSWI +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
-|MSIs and Wired IRQs|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|SBI IPI +
-https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
-|MSIs, Virtual MSIs and Wired IRQs|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC VS-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
-_(Trap and emulate)_ +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC M-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC VS-level +
-https://github.com/riscv/riscv-aia[`*AIA*`]|MTIMER +
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
-Priv Sstc +
-https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
-|=======
-
-* For Timer support, one or more ACLINT MTIMER devices are Required for OS-A platform.
-One MTIMER may be used for all harts, or multiple MTIMERs may be used with
-multiple topological groups of harts. The base address of MTIMER memory map registers
-is platform implementation-specific, however, the format of MTIMER operation parameters
-(`mtime` and `mtimecmp` registers) must be compliant with
-https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc#21-register-map[ACLINT MTIMER Register Map]
-
-* For Interrupt Controller and Software Interrupt support, one of the following three
-choices below is Required
- ** PLIC plus one or more ACLINT MSWI devices - DEPRECATED
- *** One MSWI may be used for all harts, or multiple MSWIs may be used with
-multiple topological groups of harts
- *** Only wired interrupts and M-mode IPIs are supported
- *** Virtualization is not supported
- *** This compatibly supports legacy PLIC + CLINT designs
- ** One or more AIA APLIC devices plus one or more pairs of ACLINT MSWI and ACLINT SSWI devices
- *** One MSWI/SSWI pair may be used for all harts, or multiple MSWI/SSWI
-pairs may be used with multiple topological groups of harts
- *** Only wired interrupts are supported
- *** Both M-mode and S-mode IPIs are supported
- *** Virtualization is not supported
- ** Zero, one, or more AIA APLIC devices plus per-hart AIA IMSIC devices
- *** Both wired and MSI external interrupts are supported
- *** Both M-mode and S-mode IPIs are supported via IMSICs
- *** Virtualization is supported
- *** Zero APLICs if there are no wired interrupts and only MSIs
+For example, if `timebase-frequency` is 100 MHz and the MTIME update
+frequency (i.e. hardware clock) is 25 MHz then the MTIME counter would
+increment by 4 upon every hardware clock tick.
+--
+
+===== Interrupts support
+
+The OS/A platorms can comply with one of the following four categories for
+interrupts support:
+
+* *Legacy IRQs - DEPRECATED*
+** One or more PLIC devices to support wired interrupts
+** One or more ACLINT MSWI devices to support M-mode software interrupts
+** Software interrupts for S-mode and VS-mode supported using the
+ SBI IPI extension
+** Compatibile with legacy platforms having PLIC plus CLINT devices
+** MSI external interrupts not supported
+** MSI virtualization is not supported
+* *Only Wired IRQs*
+** One or more AIA APLIC devices to support wired interrupts
+** One or more ACLINT MSWI devices to support M-mode software interrupts
+** One or more ACLINT SSWI devices to support HS-mode software interrupts
+** Software interrupts for VS-mode supported using the SBI IPI extension
+** MSI external interrupts not supported
+** MSI virtualization is not supported
+* *MSIs and Wired IRQs*
+** AIA local interrupt CSRs must be supported by each hart
+*** `mvien` and `mvip` CSRs must be implemented
+*** `hvien` and `hvip` CSRs must be implemented if H-extension is implemented
+*** `siselect` CSR must support holding a 9-bit value
+*** `vsiselect` CSR must support holding a 9-bit value if H-extension
+ is implemented
+** Per-hart AIA IMSIC devices must support MSIs for M-mode and HS-mode
+*** IPRIOLEN = 6 to 8
+*** MIFMAX = SIFMAX = 63 to 255
+*** Must support at least 63 distinct interrupt identities
+*** Must implement `seteipnum_le` memory-mapped register
+** One, or more AIA APLIC devices to support wired interrupts
+*** EIID and IID fields must be 6 to 8 bits wide matching the number of
+ interrrupt identities supported by AIA IMSIC
+** Software interrupts for M-mode and HS-mode supported using AIA IMSIC devices
+** Software interrupts for VS-mode supported using the SBI IPI extension
+** MSI virtualization is not supported
+* *MSIs, Virtual MSIs, and Wired IRQs*
+** The H-extension must be implemeted by each hart to support virtual MSIs
+*** GEILEN must be 1 or more
+** AIA local interrupt CSRs must be supported by each hart
+*** `mvien` and `mvip` CSRs must be implemented
+*** `hvien` and `hvip` CSRs must be implemented
+*** `siselect` CSR must support holding a 9-bit value
+*** `vsiselect` CSR must support holding a 9-bit value
+** Per-hart AIA IMSIC devices to support MSIs for M-mode, HS-mode and VS-mode
+*** IPRIOLEN = 6 to 8
+*** MIFMAX = SIFMAX = GIFMAX = 63 to 255
+*** Must support at least 63 distinct interrupt identities
+*** Must implement `seteipnum_le` memory-mapped register
+*** Must implement at least 1 guest interrupt file
+** One, or more AIA APLIC devices to support wired interrupts
+*** EIID and IID fields must be 6 to 8 bits wide matching the number of
+ interrrupt identities supported by AIA IMSIC
+** Software interrupts for M-mode, HS-mode and VS-mode supported using
+ AIA IMSIC devices
+** MSI virtualization is supported
+
+===== Summary
+
+The <<table_interrutps_and_timer_osa_platforms>> below summarizes the four
+categories of timer and interrupt support allowed in a OS/A platorm.
+
+[#table_interrutps_and_timer_osa_platforms]
+.Interrupts and Timer support in OS/A platforms
+[stripes="none", width="100%", cols="^2s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s"]
+|===
+.2+|+++<font size=".8em">OS-A Platform</font>+++
+3+|+++<font size=".8em">MSIs</font>+++
+3+|+++<font size=".8em">Wired Interrupts</font>+++
+3+|+++<font size=".8em">Software Interrupts</font>+++
+3+|+++<font size=".8em">Timer</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+|+++<font size=".6em">M-mode</font>+++
+|+++<font size=".6em">S-mode</font>+++
+|+++<font size=".6em">VS-mode</font>+++
+
+|+++<font size=".8em">Legacy IRQs</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">PLIC</font>+++ ^<<spec_plic>>^
+|+++<font size=".6em">PLIC</font>+++ ^<<spec_plic>>^
+|+++<font size=".6em">PLIC (emulate)</font>+++ ^<<spec_plic>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MSWI</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI Timer</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI Timer</font></color>+++ ^<<spec_sbi>>^
+
+|+++<font size=".8em">Only Wired IRQs</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<font size=".6em">NA</font>+++
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MSWI</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#6aa84f"><font size=".6em">SSWI</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+
+|+++<font size=".8em">MSIs and Wired IRQs</font>+++
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+
+|+++<font size=".8em">MSIs, Virtual MSIs and Wired IRQs</font>+++
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
+|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
+|===
==== System Peripherals
* UART/Serial Console
@@ -359,27 +419,6 @@ of the following:
** UART 16550 - _REQUIRED_
** UART 8250 - _DEPRECATED_
-* Clock and Timers
-** Platforms are required to provide an at least 10ns resolution 64-bit counter
-with strictly monotonic updates.
-** The hardware clock that drives the counter is required to operate at a minimum
-frequency of 10MHz.
-** Platforms that use DT for hardware discovery are required to advertise the
-timebase to the operating systems via the `timebase-frequency` property of the
-"/cpus" node
-footnote:[https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/riscv/cpus.yaml].
-
-[sidebar]
---
-[underline]*_Implementation Note_*
-
-For a counter with 10ns resolution the `timebase-frequency` value would be 100000000
-(100 MHz) which would also be the minimum possible value for `timebase-frequency`.
-From the software perspective a unit increment of the mtime value would correspond
-to a 10ns interval. However the hardware clock driving the counter could operate at a
-lower frequency, thereby incrementing the mtime value by more than one unit per
-clock tick.
---
==== Boot Process
- The base specification defines the interface between the firmware and the
operating system suitable for the RISC-V platforms with rich operating
@@ -449,6 +488,8 @@ base with the additional requirements as below.
The platforms which conform to server extension are required to implement +
* RV64 support
+* The `time` CSR must be implemented in hardware
+* The Sstc extension <<spec_priv_sstc>> must be implemented
* RISC-V ISA H-extension with following additional requirements:
** VMID support
** Upon load/store/AMO exceptions taken into HS-mode, the `htinst` CSR must
@@ -489,7 +530,20 @@ above.
respect to all harts connected to the DM
* Rationale: Debuggers must be able to view memory coherently
-==== Interrupt Controller
+==== Interrupts and Timer
+
+The OS-A server platform must comply with "MSIs, Virtual MSIs and Wired IRQs"
+category of interrupts and timer support defined in the base with following
+additional requirements:
+
+* The H-extension implemented by each hart must support GEILEN = 3 or more
+* Per-hart AIA IMSIC devices
+** Must implement at least 3 guest interrupt files
+** Must support at least 255 distinct interrupt identities
+** IPRIOLEN = 8

verb missing

+** MIFMAX = SIFMAX = GIFMAX = 255

verb missing

Best regards

Heinrich

+* EIID and IID fields of AIA APLIC devices must be at least 8 bits wide
+ matching the number of interrrupt identities supported by AIA IMSIC
==== Boot and Runtime Requirements
===== Firmware
@@ -659,12 +713,6 @@ implemented but it can return EFI_UNSUPPORTED.
|===
==== System Peripherals
-===== Clock and Timers
-** Platforms are required to implement the time CSR.
-** Platforms are required to implement the Sstc extension <<spec_priv_sstc>>.
-** Platforms are required to delegate the supervisor timer interrupt to 'S'
-mode. If the 'H' extension is implemented then the platforms are required to
-delegate the virtual supervisor timer interrupt to 'VS' mode.
===== Watchdog Timers
Implementation of a two-stage watchdog timer, as defined in the WatchDog Timer
@@ -897,11 +945,6 @@ in the physical RV processor. +
* Logging and/or reporting of errors can be masked. +
* PCIe AER capability is required. +
-==== Interrupt Controller, Software Interrupt, and Timer Requirements
- * For Timer support, ACLINT MTIMER devices is/are Required
- * For Interrupt Controller and Software Interrupt support, the following one choice is Required
- - Zero, one, or more AIA APLIC devices plus per-hart AIA IMSIC devices
-
// M Platform
== M Platform
diff --git a/riscv-platform-spec.yml b/riscv-platform-spec.yml
new file mode 100644
index 0000000..ce00e22
--- /dev/null
+++ b/riscv-platform-spec.yml
@@ -0,0 +1,8 @@
+extends: default
+image:
+ align: center
+caption:
+ align: center
+table:
+ caption:
+ side: bottom

On 06/08/21, 1:17 PM, "Heinrich Schuchardt" <heinrich.schuchardt@...> wrote:

On 8/6/21 8:19 AM, Anup Patel wrote:
> We re-write the interrupts and timer section to align the
> interrupts and timer table. We also add more fine grained
> requirements for AIA.
>
> Signed-off-by: Anup Patel <anup.patel@...>
> ---
> Makefile | 4 +-
> riscv-platform-spec.adoc | 323 ++++++++++++++++++++++-----------------
> riscv-platform-spec.yml | 8 +
> 3 files changed, 193 insertions(+), 142 deletions(-)
> create mode 100644 riscv-platform-spec.yml
>
> diff --git a/Makefile b/Makefile
> index 48e8fe9..ff8fbf6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -22,8 +22,8 @@ $(PLATFORM_SPEC).md: $(PLATFORM_SPEC).xml
> $(PLATFORM_SPEC).xml: $(PLATFORM_SPEC).adoc
> $(ASCIIDOCTOR) -d book -b docbook $<
>
> -$(PLATFORM_SPEC).pdf: $(PLATFORM_SPEC).adoc $(IMAGES)
> - $(ASCIIDOCTOR) -d book -r asciidoctor-pdf -b pdf $<
> +$(PLATFORM_SPEC).pdf: $(PLATFORM_SPEC).adoc $(IMAGES) $(PLATFORM_SPEC).yml
> + $(ASCIIDOCTOR) -d book -r asciidoctor-pdf -a pdf-style=$(PLATFORM_SPEC).yml -b pdf $<
>
> $(PLATFORM_SPEC).html: $(PLATFORM_SPEC).adoc $(IMAGES)
> $(ASCIIDOCTOR) -d book -b html $<
> diff --git a/riscv-platform-spec.adoc b/riscv-platform-spec.adoc
> index cffb71c..3994ef3 100644
> --- a/riscv-platform-spec.adoc
> +++ b/riscv-platform-spec.adoc
> @@ -13,6 +13,7 @@
> :doctype: book
> :sectnums:
> :sectnumlevels: 5
> +:xrefstyle: short
> :toc: macro
> :toclevels: 5
>
> @@ -235,114 +236,173 @@ each must be 1
> The default should allow code that's sensitive to these requirements to be
> debugged.
>
> -==== Interrupt Controller, Software Interrupt, and Timer Requirements
> -In the following requirements,
> -https://github.com/riscv/riscv-aia[*AIA*] refers to the Advanced Interrupt Architecture, https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[*ACLINT*]
> -refers to the Advanced *CLINT*. AIA comprises two separate components: `IMSICs` and `APLICs`.
> -If supported, there is an `IMSIC` device associated with each hart.
> -If supported, *APLIC* devices are global to all harts, and there may be one or
> -multiple in a system. *ACLINT* comprises three separate components: `MTIMER` for
> -Timer support, and `MSWI` and `SSWI` for Machine-level and Supervisor-level
> -Software Interrupt (IPI) support. +
> -https://github.com/riscv/riscv-plic-spec/blob/master/riscv-plic.adoc[*PLIC*]
> -refers to the legacy Platform-Level Interrupt Controller that provides
> -facilities to route external interrupts to a hart context with a given privilege
> -mode. The number of non-local interrupt sources supported by PLIC and how does
> -each of them connect to the hart context is PLIC core implementation-specific. +
> -*CLINT* is a legacy Core-Local Interrupt Controller that is a compatible subset of
> -ACLINT which provides facilities to trigger Software (IPI) and Timer interrupts to
> -hart.
> +==== Interrupts and Timer
> +
> +===== Timer support
> +
> +* One or more ACLINT MTIMER devices are required for the OS-A platform
> +* All MTIME counters must be 64-bit counters with a 10ns resolution (i.e.
> + an increment by 1 represents 10 ns).
> +* The MTIME update frequency (i.e. hardware clock) must be between 10 MHz
> + and 100 MHz, and updates must be strictly monotonic.
> +* Platforms must provide a way to discover MTIME resolution using appropriate
> + hardware discovery mechanism:
> +** Platforms that use DT for hardware discovery are required to advertise the
> + timebase to the operating systems via the `timebase-frequency` property of
> + the "/cpus" node
> +footnote:[https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/riscv/cpus.yaml].
> +
> +[sidebar]
> +--
> +[underline]*_Implementation Note_*
>
> -.The following table summarizes what features are supported for four classes of OS/A platforms.
> -[width="100%",cols="^,^,^,^,^,^,^,^,^,^,^,^,^"]
> -|=======
> -.2+|*OS-A Platform* 3+|*MSIs* 3+|*Wired Interrupts* 3+|*IPIs* 3+|*Timer*
> -|M-level|S-level|VS-level|M-level|S-level|VS-level|M-level|S-level|VS-level|M-level|S-level|VS-level
> -|Existing|NA|NA|NA|PLIC|PLIC|PLIC +
> -_(Trap and emulate)_|MSWI +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
> -SBI IPI +
> -https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|SBI IPI +
> -https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|SBI Timer +
> -https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|SBI Timer +
> -https://github.com/riscv/riscv-sbi-doc[`*SBI*`]
> -|Only Wired IRQs|NA|NA|NA|APLIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -_(Trap and emulate)_ +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|MSWI +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
> -SSWI +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
> -SBI IPI +
> -https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
> -Priv Sstc +
> -https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
> -Priv Sstc +
> -https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
> -|MSIs and Wired IRQs|IMSIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -_(Trap and emulate)_ +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -_(Trap and emulate)_ +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|SBI IPI +
> -https://github.com/riscv/riscv-sbi-doc[`*SBI*`]|MTIMER +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
> -Priv Sstc +
> -https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
> -Priv Sstc +
> -https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
> -|MSIs, Virtual MSIs and Wired IRQs|IMSIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC VS-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|APLIC S-level +
> -_(Trap and emulate)_ +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC M-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC S-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|IMSIC VS-level +
> -https://github.com/riscv/riscv-aia[`*AIA*`]|MTIMER +
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc[`*ACLINT*`]|
> -Priv Sstc +
> -https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]|
> -Priv Sstc +
> -https://github.com/riscv/riscv-isa-manual/releases[`*Priv Spec*`]
> -|=======
> -
> -* For Timer support, one or more ACLINT MTIMER devices are Required for OS-A platform.
> -One MTIMER may be used for all harts, or multiple MTIMERs may be used with
> -multiple topological groups of harts. The base address of MTIMER memory map registers
> -is platform implementation-specific, however, the format of MTIMER operation parameters
> -(`mtime` and `mtimecmp` registers) must be compliant with
> -https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc#21-register-map[ACLINT MTIMER Register Map]
> -
> -* For Interrupt Controller and Software Interrupt support, one of the following three
> -choices below is Required
> - ** PLIC plus one or more ACLINT MSWI devices - DEPRECATED
> - *** One MSWI may be used for all harts, or multiple MSWIs may be used with
> -multiple topological groups of harts
> - *** Only wired interrupts and M-mode IPIs are supported
> - *** Virtualization is not supported
> - *** This compatibly supports legacy PLIC + CLINT designs
> - ** One or more AIA APLIC devices plus one or more pairs of ACLINT MSWI and ACLINT SSWI devices
> - *** One MSWI/SSWI pair may be used for all harts, or multiple MSWI/SSWI
> -pairs may be used with multiple topological groups of harts
> - *** Only wired interrupts are supported
> - *** Both M-mode and S-mode IPIs are supported
> - *** Virtualization is not supported
> - ** Zero, one, or more AIA APLIC devices plus per-hart AIA IMSIC devices
> - *** Both wired and MSI external interrupts are supported
> - *** Both M-mode and S-mode IPIs are supported via IMSICs
> - *** Virtualization is supported
> - *** Zero APLICs if there are no wired interrupts and only MSIs
> +For example, if `timebase-frequency` is 100 MHz and the MTIME update
> +frequency (i.e. hardware clock) is 25 MHz then the MTIME counter would
> +increment by 4 upon every hardware clock tick.
> +--
> +
> +===== Interrupts support
> +
> +The OS/A platorms can comply with one of the following four categories for
> +interrupts support:
> +
> +* *Legacy IRQs - DEPRECATED*
> +** One or more PLIC devices to support wired interrupts
> +** One or more ACLINT MSWI devices to support M-mode software interrupts
> +** Software interrupts for S-mode and VS-mode supported using the
> + SBI IPI extension
> +** Compatibile with legacy platforms having PLIC plus CLINT devices
> +** MSI external interrupts not supported
> +** MSI virtualization is not supported
> +* *Only Wired IRQs*
> +** One or more AIA APLIC devices to support wired interrupts
> +** One or more ACLINT MSWI devices to support M-mode software interrupts
> +** One or more ACLINT SSWI devices to support HS-mode software interrupts
> +** Software interrupts for VS-mode supported using the SBI IPI extension
> +** MSI external interrupts not supported
> +** MSI virtualization is not supported
> +* *MSIs and Wired IRQs*
> +** AIA local interrupt CSRs must be supported by each hart
> +*** `mvien` and `mvip` CSRs must be implemented
> +*** `hvien` and `hvip` CSRs must be implemented if H-extension is implemented
> +*** `siselect` CSR must support holding a 9-bit value
> +*** `vsiselect` CSR must support holding a 9-bit value if H-extension
> + is implemented
> +** Per-hart AIA IMSIC devices must support MSIs for M-mode and HS-mode
> +*** IPRIOLEN = 6 to 8
> +*** MIFMAX = SIFMAX = 63 to 255
> +*** Must support at least 63 distinct interrupt identities
> +*** Must implement `seteipnum_le` memory-mapped register
> +** One, or more AIA APLIC devices to support wired interrupts
> +*** EIID and IID fields must be 6 to 8 bits wide matching the number of
> + interrrupt identities supported by AIA IMSIC
> +** Software interrupts for M-mode and HS-mode supported using AIA IMSIC devices
> +** Software interrupts for VS-mode supported using the SBI IPI extension
> +** MSI virtualization is not supported
> +* *MSIs, Virtual MSIs, and Wired IRQs*
> +** The H-extension must be implemeted by each hart to support virtual MSIs
> +*** GEILEN must be 1 or more
> +** AIA local interrupt CSRs must be supported by each hart
> +*** `mvien` and `mvip` CSRs must be implemented
> +*** `hvien` and `hvip` CSRs must be implemented
> +*** `siselect` CSR must support holding a 9-bit value
> +*** `vsiselect` CSR must support holding a 9-bit value
> +** Per-hart AIA IMSIC devices to support MSIs for M-mode, HS-mode and VS-mode
> +*** IPRIOLEN = 6 to 8
> +*** MIFMAX = SIFMAX = GIFMAX = 63 to 255
> +*** Must support at least 63 distinct interrupt identities
> +*** Must implement `seteipnum_le` memory-mapped register
> +*** Must implement at least 1 guest interrupt file
> +** One, or more AIA APLIC devices to support wired interrupts
> +*** EIID and IID fields must be 6 to 8 bits wide matching the number of
> + interrrupt identities supported by AIA IMSIC
> +** Software interrupts for M-mode, HS-mode and VS-mode supported using
> + AIA IMSIC devices
> +** MSI virtualization is supported
> +
> +===== Summary
> +
> +The <<table_interrutps_and_timer_osa_platforms>> below summarizes the four
> +categories of timer and interrupt support allowed in a OS/A platorm.
> +
> +[#table_interrutps_and_timer_osa_platforms]
> +.Interrupts and Timer support in OS/A platforms
> +[stripes="none", width="100%", cols="^2s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s,^1s"]
> +|===
> +.2+|+++<font size=".8em">OS-A Platform</font>+++
> +3+|+++<font size=".8em">MSIs</font>+++
> +3+|+++<font size=".8em">Wired Interrupts</font>+++
> +3+|+++<font size=".8em">Software Interrupts</font>+++
> +3+|+++<font size=".8em">Timer</font>+++
> +|+++<font size=".6em">M-mode</font>+++
> +|+++<font size=".6em">S-mode</font>+++
> +|+++<font size=".6em">VS-mode</font>+++
> +|+++<font size=".6em">M-mode</font>+++
> +|+++<font size=".6em">S-mode</font>+++
> +|+++<font size=".6em">VS-mode</font>+++
> +|+++<font size=".6em">M-mode</font>+++
> +|+++<font size=".6em">S-mode</font>+++
> +|+++<font size=".6em">VS-mode</font>+++
> +|+++<font size=".6em">M-mode</font>+++
> +|+++<font size=".6em">S-mode</font>+++
> +|+++<font size=".6em">VS-mode</font>+++
> +
> +|+++<font size=".8em">Legacy IRQs</font>+++
> +|+++<font size=".6em">NA</font>+++
> +|+++<font size=".6em">NA</font>+++
> +|+++<font size=".6em">NA</font>+++
> +|+++<font size=".6em">PLIC</font>+++ ^<<spec_plic>>^
> +|+++<font size=".6em">PLIC</font>+++ ^<<spec_plic>>^
> +|+++<font size=".6em">PLIC (emulate)</font>+++ ^<<spec_plic>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">MSWI</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
> +|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#e06666"><font size=".6em">SBI Timer</font></color>+++ ^<<spec_sbi>>^
> +|+++<color rgb="#e06666"><font size=".6em">SBI Timer</font></color>+++ ^<<spec_sbi>>^
> +
> +|+++<font size=".8em">Only Wired IRQs</font>+++
> +|+++<font size=".6em">NA</font>+++
> +|+++<font size=".6em">NA</font>+++
> +|+++<font size=".6em">NA</font>+++
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">MSWI</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">SSWI</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
> +|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
> +
> +|+++<font size=".8em">MSIs and Wired IRQs</font>+++
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC (emulate)</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#e06666"><font size=".6em">SBI IPI</font></color>+++ ^<<spec_sbi>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
> +|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
> +
> +|+++<font size=".8em">MSIs, Virtual MSIs and Wired IRQs</font>+++
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">APLIC (emulate)</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#738dc5"><font size=".6em">IMSIC</font></color>+++ ^<<spec_aia>>^
> +|+++<color rgb="#6aa84f"><font size=".6em">MTIMER</font></color>+++ ^<<spec_aclint>>^
> +|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
> +|+++<color rgb="#e69138"><font size=".6em">Priv Sstc</font></color>+++ ^<<spec_priv_sstc>>^
> +|===
>
> ==== System Peripherals
> * UART/Serial Console
> @@ -359,27 +419,6 @@ of the following:
> ** UART 16550 - _REQUIRED_
> ** UART 8250 - _DEPRECATED_
>
> -* Clock and Timers
> -** Platforms are required to provide an at least 10ns resolution 64-bit counter
> -with strictly monotonic updates.
> -** The hardware clock that drives the counter is required to operate at a minimum
> -frequency of 10MHz.
> -** Platforms that use DT for hardware discovery are required to advertise the
> -timebase to the operating systems via the `timebase-frequency` property of the
> -"/cpus" node
> -footnote:[https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/riscv/cpus.yaml].
> -
> -[sidebar]
> ---
> -[underline]*_Implementation Note_*
> -
> -For a counter with 10ns resolution the `timebase-frequency` value would be 100000000
> -(100 MHz) which would also be the minimum possible value for `timebase-frequency`.
> -From the software perspective a unit increment of the mtime value would correspond
> -to a 10ns interval. However the hardware clock driving the counter could operate at a
> -lower frequency, thereby incrementing the mtime value by more than one unit per
> -clock tick.
> ---
> ==== Boot Process
> - The base specification defines the interface between the firmware and the
> operating system suitable for the RISC-V platforms with rich operating
> @@ -449,6 +488,8 @@ base with the additional requirements as below.
> The platforms which conform to server extension are required to implement +
>
> * RV64 support
> +* The `time` CSR must be implemented in hardware
> +* The Sstc extension <<spec_priv_sstc>> must be implemented
> * RISC-V ISA H-extension with following additional requirements:
> ** VMID support
> ** Upon load/store/AMO exceptions taken into HS-mode, the `htinst` CSR must
> @@ -489,7 +530,20 @@ above.
> respect to all harts connected to the DM
> * Rationale: Debuggers must be able to view memory coherently
>
> -==== Interrupt Controller
> +==== Interrupts and Timer
> +
> +The OS-A server platform must comply with "MSIs, Virtual MSIs and Wired IRQs"
> +category of interrupts and timer support defined in the base with following
> +additional requirements:
> +
> +* The H-extension implemented by each hart must support GEILEN = 3 or more
> +* Per-hart AIA IMSIC devices
> +** Must implement at least 3 guest interrupt files
> +** Must support at least 255 distinct interrupt identities
> +** IPRIOLEN = 8

verb missing

> +** MIFMAX = SIFMAX = GIFMAX = 255

verb missing

[Anup] Okay, will update.

Regards,
Anup

Best regards

Heinrich

> +* EIID and IID fields of AIA APLIC devices must be at least 8 bits wide
> + matching the number of interrrupt identities supported by AIA IMSIC
>
> ==== Boot and Runtime Requirements
> ===== Firmware
> @@ -659,12 +713,6 @@ implemented but it can return EFI_UNSUPPORTED.
> |===
>
> ==== System Peripherals
> -===== Clock and Timers
> -** Platforms are required to implement the time CSR.
> -** Platforms are required to implement the Sstc extension <<spec_priv_sstc>>.
> -** Platforms are required to delegate the supervisor timer interrupt to 'S'
> -mode. If the 'H' extension is implemented then the platforms are required to
> -delegate the virtual supervisor timer interrupt to 'VS' mode.
>
> ===== Watchdog Timers
> Implementation of a two-stage watchdog timer, as defined in the WatchDog Timer
> @@ -897,11 +945,6 @@ in the physical RV processor. +
> * Logging and/or reporting of errors can be masked. +
> * PCIe AER capability is required. +
>
> -==== Interrupt Controller, Software Interrupt, and Timer Requirements
> - * For Timer support, ACLINT MTIMER devices is/are Required
> - * For Interrupt Controller and Software Interrupt support, the following one choice is Required
> - - Zero, one, or more AIA APLIC devices plus per-hart AIA IMSIC devices
> -
> // M Platform
> == M Platform
>
> diff --git a/riscv-platform-spec.yml b/riscv-platform-spec.yml
> new file mode 100644
> index 0000000..ce00e22
> --- /dev/null
> +++ b/riscv-platform-spec.yml
> @@ -0,0 +1,8 @@
> +extends: default
> +image:
> + align: center
> +caption:
> + align: center
> +table:
> + caption:
> + side: bottom
>