I'm essentially trying to swap the RAM modules between the two cores on the STM32H755 so that all data in RAM used by the M7 is in SRAM1-3 and for the M4 is in AIXISRAM, but I'm observing some issues in startup behavior on the M4.
From my understanding of the manual and application notes: the M7 uses the AXISRAM by default (both in D1 domain) and M4 uses SRAM1-3 by default (all D2 domain), but either processor *should* be able to access either domain's RAM.
I have made the following set of incremental changes based on functional testing and guidance in Section 9.5.9 "General clock concept overview" from the manual:
1. Change: Updated linker files (M7 now uses SRAM starting at 0x10000000 and sized 288K for `.bss`, `.data`, and user heap; M4 uses RAM_D1 starting at 0x24000000 and sized 512K):
- Result: Builds succeed for both M4 and M7 targets, but hardfault observed on M7 at startup before debugger reaches M7's `main()`
2. Change: Updated `SystemInit()` in system_stm32h7xx_dualcore_boot_cm4_cm7.c to enable AXISRAM access from M4 via RCC->AHB3ENR and SRAM1-3 access from M7 via RCC->AHB2ENR
- Result: `SystemInit()` completes and debugger reaches M7’s main(). Software times out in main() in Boot_Mode_Sequence_1 block when waiting for M4 to boot and enter in stop mode, Error_Handler() is called
/* AXISRAM block enable - Indicate that AXISRAM is allocated by the M4 */
RCC->AHB3ENR |= RCC_AHB3ENR_AXISRAMEN;
/* SRAMx block enable - Indicate that the 3 SRAM Modules allocated by the M7 */
RCC->AHB2ENR |= (RCC_AHB2ENR_SRAM1EN | RCC_AHB2ENR_SRAM2EN | RCC_AHB2ENR_SRAM3EN);
I'm now stuck - the M7 now executes `main()` but stalls and times out waiting for the M4 to enter stop mode and set `RCC_FLAG_D2CKRDY` to `RESET`.
It seems that the M4 application is not being started. I am able to load and start it via debugger after the initial programming, but I observe a sigtrap in the `Reset_Handler` when attempting to jump to the application's entrypoint (e.g. `main()`).
Is it possible to completely swap the RAM modules like this? What piece could I be missing?
What could be preventing the M4 from starting?
