From: Abner Chang <abner.chang@...>

Initial version of Interrupt Controller, Software Interrupt,
and Timer Requirements. This patch combines the text sent out
by Kumar and the patch Abner sent previously.

Signed-off-by: Abner Chang <renba.chang@...>
Cc: Kumar Sankaran <ksankaran@...>
Cc: Anup Patel <anup.patel@...>
Signed-off-by: Abner Chang <abner.chang@...>
---
riscv-platform-spec.adoc | 78 +++++++++++++++++++++++++++++++++++++---
1 file changed, 73 insertions(+), 5 deletions(-)

diff --git a/riscv-platform-spec.adoc b/riscv-platform-spec.adoc
index 87ab7f8..8a1a45f 100644
--- a/riscv-platform-spec.adoc
+++ b/riscv-platform-spec.adoc
@@ -64,8 +64,14 @@ The M platform has the following extensions:
|EE | Execution Environment
|OSPM | Operating System Power Management
|RV32GC | RISC-V 32-bit general purpose ISA described as RV32IMAFDC.
-|RV64GC | RISC-V 64-bit general purpose ISA described as RV64IMAFDC.
+|RV64GC | RISC-V 64-bit general purpose ISA described as RV64IMAFDC.
|RAS | Reliability, Availability, and Serviceability
+|CLINT | Legacy Core-Local Interrupt Controller
+|ACLINT | Advanced CLINT
+|PLIC | Legacy Platform-Level Interrupt Controller
+|APLIC | Advanced PLIC
+|AIA | Advanced Interrupt Architecture
+|IMSIC | Incomning MSI Controller
|===

=== Specifications
@@ -179,10 +185,67 @@ each must be 1
The default should allow code that's sensitive to these requirements to be
debugged.

-==== Interrupt Controller
-* AIA
-* PLIC + CLINT
-* Interrupt Assignments
+==== Interrupt Controller, Software Interrupt, and Timer Requirements
+In the following requirements,
+*AIA* (spec link ?) 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.
+
+.The following table summarizes what features are supported for three 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 Platforms|NA|NA|NA|PLIC|PLIC|PLIC|MSWI +
+(CLINT)|SBI IPI|SBI IPI|MTIMER +
+(CLINT)|SBI Timer|SBI Timer
+|Platfomrs with only wired IRQs|NA|NA|NA|APLIC M-level Domain|APLIC S-level Domain|
+APLIC S-level Domain|MSWI|SSWI|SBI IPI|MTIMER|Priv SSTC|Priv SSTC
+|Platfomrs with MSIs and wired IRQs|IMSIC M-level|IMSIC S-level|IMSIC VS-level|
+APLIC M-level Domain|APLIC S-level Domain|APLIC S-level Domain|IMSIC M-level|
+IMSIC S-level|IMSIC VS-level +
+OR +
+SBI IPI|MTIMER|Priv SSTC|Priv SSTC
+|=======
+
+* 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

==== System Peripherals
* UART/Serial Console
@@ -513,6 +576,11 @@ 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

--
2.19.0.windows.1