Re: [PATCH v1 2/2] Section 3.1.4 System Peripherals.


atishp@...
 

On Sun, 2021-04-11 at 20:32 +0530, Mayuresh Chitale wrote:
This patch is an initial draft for the section
3.1.4 - System Peripherals.

Signed-off-by: Mayuresh Chitale <mchitale@...>
---
 riscv-platform-spec.adoc | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/riscv-platform-spec.adoc b/riscv-platform-spec.adoc
index 003181c..f164545 100644
--- a/riscv-platform-spec.adoc
+++ b/riscv-platform-spec.adoc
@@ -52,10 +52,33 @@ include::profiles.adoc[]
 * Interrupt Assignments
 
 ==== System Peripherals
-* UART/Serial Console
-* Clocks
-* Timers
-* Watchdog Timers
+* *UART/Serial Console* +
+In order to facilitate the bringup and debug of the low level
initial platform
+software(firmware, bootloaders, kernel etc), the platform shall
implement a UART
+port compatible with PC16550D.
+* *Clock and Timers* +
+** Platforms shall provide a 10ns resolution 64-bit counter with
strictly monotonic updates.
+** The counter shall have a minimum update frequency of 10MHz.
+** Platforms shall implement the time CSR.
+** Platforms shall advertise the timebase to the operating systems
via the
+`timebase-frequency` DT property.
+** Platforms shall implement the
+https://lists.riscv.org/g/tech-privileged/message/404[Sstc] extensio
n.
+** Platforms shall delegate the supervisor timer interrupt to 'S'
mode and if
+the 'H' extension is implemented, the virtual supervisor timer
interrupt to 'VS' mode.
+
+* Watchdog Timers +
+** Platforms shall implement a two stage watchdog timer.
As the base specification also targets the dev boards, academia FPGAs
at least for Linux 2022, do we need to mandate a watchdog timer.

May be put it as strongly recommended and mandate it in Linux 2024
specification ?

+** The software shall periodically update the watchdog stage 1 value
to a
+future moment.
+** If the mtime/time increments past the watchdog stage 1 compare
value then an
+interrupt shall be raised and routed to a RISC V hart and the
watchdog stage 2
+shall be activated.
+** If the mtime/time increments past the watchdog stage 2 compare
value an
+interrupt shall be raised and routed to an external hardware unit
such as a
+BMC to affect a system reset. 
Is it only intended for server extension as BMCs are common in servers
? We may need to clarify what happens in absence of a BMC ?

If the watchdog stage1 compare value was updated
+before such an event occurred then the watchdog stage 1 interrupt
shall be
+deasserted and the watchdog stage 2 shall be deactivated.
 
 ==== Boot Process
 * Firmware
--
Regards,
Atish

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