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ESawa.1
ESawa.1
Associate III
August 11, 2021
Question

STM32H750 MPU XiP

  • August 11, 2021
  • 4 replies
  • 2955 views

Hey together,

I have a question regarding MPU settings for an external QuadSPI Flash. We have a project where the full application code is placed onto the 4MB Quad SPI Flash memory W25Q32JVSIM. We have set up the QuadSPI in MemoryMapped moded and placed the application into the location 0x90000000. So far everything is fine and works as expected. Now we want to setup the MPU correct for this section. The only thing I found was in the document AN4760 on page 46. There is the follwoing indicated:

0693W00000D2Al3QAF.pngSo I set up the region as follows:

MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER3;
 MPU_InitStruct.BaseAddress = 0x90000000;
 MPU_InitStruct.Size = MPU_REGION_SIZE_4MB;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
 MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_ENABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_SHAREABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_NOT_CACHEABLE;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
 
 HAL_MPU_ConfigRegion(&MPU_InitStruct);
 /* Enables the MPU */
 HAL_MPU_Enable(MPU_PRIVILEGED_DEFAULT);

Is this the correct setting for code execution from an external quad-spi memory?

By the way: There is another region defined which prevents the access to the rest of the unsed area.

Many thanks in advance,

Eric

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    4 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    August 11, 2021

    See STM32Cube_FW_H7_V1.8.0\Projects\STM32H750B-DK\Demonstrations\MenuLauncher\Core\Src\main.c

    static void MPU_Config(void)
{
 MPU_Region_InitTypeDef MPU_InitStruct;
 
 /* Disable the MPU */
 HAL_MPU_Disable();
 
...
 
 /* Configure the MPU attributes for Quad-SPI area to strongly ordered
 This setting is essentially needed to avoid MCU blockings!
 See also STM Application Note AN4861 */
 MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.BaseAddress = QSPI_BASE_ADDRESS;
 MPU_InitStruct.Size = MPU_REGION_SIZE_256MB;
 MPU_InitStruct.AccessPermission = MPU_REGION_NO_ACCESS;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_NOT_CACHEABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_NOT_SHAREABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER1;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
 MPU_InitStruct.SubRegionDisable = 0x00;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_DISABLE;
 HAL_MPU_ConfigRegion(&MPU_InitStruct);
 
 /* Configure the MPU attributes for the QSPI 128MB to Cacheable WT */
 MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.BaseAddress = QSPI_BASE_ADDRESS;
 MPU_InitStruct.Size = MPU_REGION_SIZE_128MB;
 MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_CACHEABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_NOT_SHAREABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER2;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
 MPU_InitStruct.SubRegionDisable = 0x00;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_DISABLE;
 HAL_MPU_ConfigRegion(&MPU_InitStruct);
 
...
 /* Configure the MPU attributes for the QSPI 2MB to Cacheable WT with instruction access */
 MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.BaseAddress = QSPI_BASE_ADDRESS;
 MPU_InitStruct.Size = MPU_REGION_SIZE_2MB;
 MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_CACHEABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_NOT_SHAREABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER4;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
 MPU_InitStruct.SubRegionDisable = 0x00;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_ENABLE;
 HAL_MPU_ConfigRegion(&MPU_InitStruct);
 
...
 HAL_MPU_Enable(MPU_PRIVILEGED_DEFAULT);
}

    I don't think this is perfect, but does implement a tiered approach.

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    Tesla DeLorean
    Tesla DeLorean
    Guru
    August 11, 2021

    See Pg 88 onward, I'd lean to setting the QPSI to Read-Only, I don't see why Write-Thru is needed

    https://www.st.com/resource/en/application_note/dm00287603-lcdtft-display-controller-ltdc-on-stm32-mcus-stmicroelectronics.pdf

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    ESawa.1
    ESawa.1Author
    Associate III
    August 11, 2021

    Hey Tesla,

    thanks a lot. Regarding region1, this is clear this is to prevent speculative access on the unused area. Region2 seems to be for data or similar. But for Region4, I am a bit confused now. It seems that there are 3 different settings for similar applications:

    From your post:

    When I check here Region4, which is the most interessting one as I want to execute code, I see that there the area is set to "Normal, write through, no write allocate".

     MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.BaseAddress = QSPI_BASE_ADDRESS;
 MPU_InitStruct.Size = MPU_REGION_SIZE_2MB;
 MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_CACHEABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_NOT_SHAREABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER4;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
 MPU_InitStruct.SubRegionDisable = 0x00;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_ENABLE;
 HAL_MPU_ConfigRegion(&MPU_InitStruct);

    AN4760 on page 46:

    They recommend to set it as strongly ordered memory which would be: 

     MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.BaseAddress = 0x90000000;
 MPU_InitStruct.Size = MPU_REGION_SIZE_4MB;
 MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_NOT_CACHEABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_SHAREABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER4;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
 MPU_InitStruct.SubRegionDisable = 0x00;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_ENABLE;
 HAL_MPU_ConfigRegion(&MPU_InitStruct);

    From STM32 MPU tips video:

    https://www.youtube.com/watch?v=6IUfxSAFhlw --> time: 16:02

    There they recommend to set it as "Normal, write and read allocate"

     MPU_InitStruct.Enable = MPU_REGION_ENABLE;
 MPU_InitStruct.Number = MPU_REGION_NUMBER4;
 MPU_InitStruct.BaseAddress = 0x90000000;
 MPU_InitStruct.Size = MPU_REGION_SIZE_4MB;
 MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL1;
 MPU_InitStruct.AccessPermission = MPU_REGION_FULL_ACCESS;
 MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_ENABLE;
 MPU_InitStruct.IsShareable = MPU_ACCESS_SHAREABLE;
 MPU_InitStruct.IsCacheable = MPU_ACCESS_CACHEABLE;
 MPU_InitStruct.IsBufferable = MPU_ACCESS_BUFFERABLE;
 
 HAL_MPU_ConfigRegion(&MPU_InitStruct);

    But what is the right one for executing code?

    Sorry for my confusion.

    Many thanks in advance,

    Eric

    Tesla DeLorean
    Tesla DeLorean
    Guru
    August 11, 2021

    I think the first is a catch-all processed first (NO_ACCESS) to establish how the memory should be dealt with

    I think you want caching, but not buffering or writing.

    Most part you want full device accessible for XIP, one could perhaps partition in linker script to add some protection, but would need consistent application.

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