How to correctly reassign RAM on STM32H755 for M4 to use AXISRAM and M7 to use SRAM1

[agomken]

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?

[Tesla DeLorean]

Is it even necessary? Aren't these things dual-ported?

Make sure the linker scripts don't use the same memory regions, so the system isn't conflicted about who gets to manage the content.

Make sure the initial stack is in a memory that's clocks are already enabled. You can move it elsewhere once the clocks are running.

[agomken]

I'm confident that there are no conflicts from my linker files, and I'm sure that clocks are enabled and running. It seems that you're confirming that this should be possible, so I would appreciate any insight from the ST community on what could preventing the M4 from starting. I've edited my original post to improve clarity.

As I stated in my post, the M7 is definitely starting but is getting hung waiting for the M4 to start and enter stop mode. Something is preventing the M4 Reset_Handler from starting `main()`, but I'm not sure what. This is what I'm seeking help/input in resolving.

[GWatk.1]

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