Variables not properly initialized when using data relocation with SDRAM

[hjuul]

When using data relocation to store variables in external SDRAM the kernel will initialize the data section from ROM and clear the bss section. But this is done before the SDRAM is initialized, so the data will not be retained. In my application I see that all variables that are stored in SDRAM have wrong initialization values.

I'm seeing this with an stm32f7, using driver memc_stm32_sdram.c. This driver has the initialization level POST_KERNEL. I have verified that kernel/init.c and kernel/xip.c correctly initialize the relocated data, and also that the data is lost during memc_stm32_sdram_init().

As a workaround I'm calling bss_zeroing_relocation() and data_copy_xip_relocation() at the end of memc_stm32_sdram_init(). This fixes the problem for me, but it is not a general solution because it may overwrite any other data relocated to internal RAM.

One possible solution to this is to initialize the SDRAM a lot earlier, but that will probably require a rewrite of the driver (to not depend on kernel, clock initalization, etc)

Environment

• OS: Linux
• Toolchain: Zephyr SDK 0.13.1
• Zephyr v2.7.0

[erwango]

Thanks @hjuul for raising this. Would you be able to provide some sample (in a PR for instance) code + board config or test branch to save time in reproducing the issue ?

[hjuul]

@erwango , I've created a demonstration for this based on samples/application_development/code_relocation. I've tested it on stm32f769i_disco and it fails. You can find it in my zephyr fork:
https://github.com/hjuul/zephyr/tree/reproduce/43555

To reproduce on that branch:

west build zephyr/samples/application_development/code_relocation -b stm32f769i_disco 
west flash

When running this, somewhere in the output you should see something like:

***** var_sdram_data=558401858, expected 10
***** var_sdram_bss=-2147326859, expected 0

Now, if you revert the CMakeLists.txt file that I've modified, so that the relocation is not to SDRAM, you will see that variables are correctly initialized.

[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.

[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.

[hjuul]

Please remove the stale label, this is a quite critical bug.