I have been trying for a while now to do something simular to this with threadx
https://community.st.com/t5/stm32-mcus/how-to-use-stm32u5-with-freertos-in-tickless-mode/tac-p/857701#M1715
I want to be able to put the MCU into STOP and wake from uart traffic, I am using threadx not freertos. I should note here that I have written a lot of code on the STM32U575 in the last couple years and have used threadx successfully quite a few times. Ultimately I want to add this to FW that is already running on a product so I would rather not change to freertos. For the purposes of figuring this out I am working on the nucleo board.
The problem I am encountering is that the MCU never enters Stop at all unless I kill SRAM3. As a sanity check I also tried doing this without an RTOS:
https://community.st.com/t5/stm32-mcus/how-to-wake-up-the-stm32u5-from-stop2-using-lpuart/ta-p/49436
Its the same thing as the first link just without freertos or my threadx adaptation. It works fine!
So I took a step back and spent some time fooling around with this application example that ST includes and discovered some things:
https://github.com/STMicroelectronics/STM32CubeU5/blob/main/Projects/NUCLEO-U5A5ZJ-Q/Applications/ThreadX/Tx_LowPower/Src/app_threadx.c
The application from the Tx_LowPower example does indeed get to stop but kills almost everything: clocks, io, memory, etc! However I have discovered that just by changing one Line I can get it to break in a way that it never enters stop and completely skips over the __WFI() macro
Any time the following code is called before calling HAL_PWREx_EnterSTOP2Mode(PWR_STOPENTRY_WFI); The MCU will go into stop fine... this is also what is done in the above TX_lowPower application.. but if I understand it properly it nukes SRAM3 while preserving SRAM2
MODIFY_REG(RCC->AHB2ENR1, (0xFFFFFFFFU), RCC_AHB2ENR1_SRAM2EN );
MODIFY_REG(RCC->AHB2SMENR1, (0xFFFFFFFFU), RCC_AHB2SMENR1_SRAM2SMEN);
HOWEVER!! If I comment those lines out OR change them to
MODIFY_REG(RCC->AHB2ENR1, (0xFFFFFFFFU), RCC_AHB2ENR1_SRAM2EN | RCC_AHB2ENR1_SRAM3EN);
MODIFY_REG(RCC->AHB2SMENR1, (0xFFFFFFFFU), RCC_AHB2SMENR1_SRAM2SMEN | RCC_AHB2SMENR1_SRAM3SMEN );
I can no longer enter stop mode.
Does anyone know the secret magic to entering stop mode while retaining SRAM3 using threadx?
