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


Mayuresh Chitale
 




On Fri, Apr 23, 2021 at 5:19 AM Atish Patra <Atish.Patra@...> wrote:
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 ?
We can rephrase it to : " If the mtime/time increments past the watchdog stage 2 compare value then a system reset shall occur" 

> 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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