On 4/11/21 11:02 AM, 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.

This is the first mention of DT AFAICT, so we should clarify where it
comes from and what the relevant specifications are. Should we wait to
use whatever [1] standardizes on? Will we need to be forward-compatible
in this regard?

--Sean

[1] https://github.com/riscv/configuration-structure

+** Platforms shall implement the
+https://lists.riscv.org/g/tech-privileged/message/404[Sstc] extension.
+** 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.
+** 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. 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