On a secured STM32H7Sx device (in CLOSED or LOCKED product state), what is the recommended way of passing volatile data to lower HDPL levels?
According to the reference manual, the SBS_RSSCMDR register can be used to pass volatile data from HDPL 1, 2 or 3 to HDPL 0 (RSS), so that part of the answer is covered:
Bits 15:0 RSSCMD[15:0]: RSS command
The application can use this bitfield to pass on a command to the RSS, executed at the
next reset.
But what if you want to pass volatile data from HDPL 2 or 3 to HDPL 1?
(E.g., HDPL 2 wants to call into HDPL 1 so HDPL 2 first needs to write some volatile command somewhere, then execute a reset, then HDPL 0 (RSS) boots, then HDPL 1 boots and picks up the volatile command from somewhere.)
SBS_RSSCMDR cannot be used because RSS will interpret this value as well, and RSS might clear this value at the moment it boots HDPL 1.
