Posted on May 17, 2011 at 14:26Required MPU basic operation:
1)
Protect a section of RAM.
2)
Access the RAM.
3)
Run the exception routine
My setup is a motor-control application presently utilising timer interrupts, A2D interrupts, and DMA transfers - STM32F103VG, has MPU/has 96kB RAM, all working nicely, except a demo MPU feature:
#define SIZEOF_PROTMEM 0x4000 //16kB;
#define ADDRESS_OF_PROTECTED_SRAM (SRAM_BASE + 0x14000)
volatile __root __no_init u32 au32MyProtectedBuffer[SIZEOF_PROTMEM/sizeof(u32)] @ ADDRESS_OF_PROTECTED_SRAM;
//Disable MPU
MPU_Disable();
//Turn off all regions - the reset states for the ENA bits are undefined.
//No-one else seems to do this – but just for fun OK?
for(u32 u32Rgn=0 ; u32Rgn < ((MPU->TYPE&MPU_TYPE_DREGION_Msk) >> MPU_TYPE_DREGION_Pos) ; u32Rgn++)
{
MPU->RNR = MPU_RNR_REGION_Msk & (u32Rgn << MPU_RNR_REGION_Pos);
MPU->RASR = 0;
};
//
//Configure a no access MPU region for the 16 KB of RAM.
//This region is used for demonstrating an MPU exception.
//
sMPUInit.regionEnable = TRUE;
sMPUInit.regionNo = 0;
sMPUInit.baseAddress = ADDRESS_OF_PROTECTED_SRAM;
sMPUInit.size = mpuRegionSize16Kb;
sMPUInit.accessPermission = mpuRegionNoAccess;
sMPUInit.disableExec = TRUE;
sMPUInit.shareable = FALSE;
sMPUInit.cacheable = TRUE;
sMPUInit.bufferable = TRUE;
sMPUInit.srd = 0xFF;
sMPUInit.tex = 0;
MPU_ConfigureRegion(&sMPUInit);
//Enable the Memory Manage Handler
NVIC_SystemHandlerPriorityConfig(SystemHandler_MemoryManage, 2, 8);
//Enable memory protection and mem fault exceptions – background is Priv-mode open access – courtesy MPU_CTRL_PRIVDEFENA bit.
MPU_Enable(MPU_CTRL_ENABLE_Msk | MPU_CTRL_PRIVDEFENA_Msk);
My trip code:
void SimulateMemoryViolation(void)
{
//Access the forbidden memory!
au32MyProtectedBuffer[0]++;
}
My exception handler which is not being called when I call
SimulateMemoryViolation(),
called from stub in
MemManage_Handler():
void EH_MemoryViolation(void)
{
SCB->SHCSR &= ~SCB_SHCSR_MEMFAULTACT; //clear the fault flag
//Go to infinite loop when Memory Manage exception occurs
SetScreen_MPU_Error();
}
Other symptoms: In other variations of this setup (ie. specify code blocks, peripheral blocks, User/Priv permissions etc) I can generate MPU exceptions, or hard faults , but not from accessing my “protected ram.�?
