STM32F7 Data Cache Question

Posted on September 29, 2015 at 10:10

Using MPU?

https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=https%3a%2f%2fmy.st.com%2fpublic%2fSTe2ecommunities%2fmcu%2fLists%2fcortex_mx_stm32%2fSTM32F7%20NOR%20memory%20with%20FMC&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&currentviews=145

JW

Posted on September 29, 2015 at 11:02

Hi dimitrov.valentin,

You can modify memory region altering MPU attributes.

I'd highly recommend you to have a look to the MPU project under STM32Cube F7 package:

STM32Cube_FW_F7_V1.1.0\Projects\STM32756G_EVAL\Examples\Cortex\CORTEXM_MPU, it can be very useful.

-Syrine-

Posted on September 29, 2015 at 13:04

Here's my code for the MPU initialization

static void MPU_Config(void)

 

{

 

  MPU_Region_InitTypeDef MPU_InitStruct;

 

 

 

  /* Disable the MPU */

 

  HAL_MPU_Disable();

 

 

  /* Configure the MPU attributes as WT for SRAM */

 

  MPU_InitStruct.Enable = MPU_REGION_ENABLE;

 

  MPU_InitStruct.BaseAddress = 0x20010000;

 

  MPU_InitStruct.Size = MPU_REGION_SIZE_256KB;

 

  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_NOT_SHAREABLE;

 

  MPU_InitStruct.Number = MPU_REGION_NUMBER0;

 

  MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;

 

  MPU_InitStruct.SubRegionDisable = 0x00;

 

    

 

  MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_ENABLE;

 

    

 

  HAL_MPU_ConfigRegion(&MPU_InitStruct);

 

  /* Enable the MPU */

 

  HAL_MPU_Enable(MPU_PRIVILEGED_DEFAULT);

 

}

I have a timer triggering ADC conversions every 4 seconds and DMA2 is collecting 12 samples in adc_buf.

When adc_buf is placed for example on address 0x20040000 (0x20010000 + 192K) or higher the data is cached and i only see the default values with which adc_buf was initialized.

If adc_buf is placed on addresses between 0x2001000 and 0x2003fc00 it seems to work :) i can see the new samples values every 4 seconds.

When i disable the data cache the problem disappear.

Posted on September 30, 2015 at 10:17

It appears that there is an error in the ST F7 examples. According to ARM

v7-M Architecture Reference Manual:

 

''The base address, size and attributes of a region are all configurable, with the general rule that all regions are

 

naturally aligned. This can be stated as:

 

RegionBaseAddress[(N-1):0] = 0, where N is log2(SizeofRegion_in_bytes)''

which is not correct for base address 0x20010000 and region size of 256KB.

So in this case 4 regions of 64KB must be initialized in the MPU with base addresses:

0x20010000

0x20020000

0x20030000

0x20040000