Posted on November 12, 2017 at 17:55
I want to protect a memory region from writing. I've configured MPU, but it is not generating any faults. The base address of the region that I want to protect is 0x20000000. The region size is 64 bytes.
Here's how I did it,
//Memory Protection Unit Registers
#define MPU_CTRL (*((volatile unsigned long*) 0xE000ED94))
#define MPU_RNR (*((volatile unsigned long*) 0xE000ED98))
#define MPU_RBAR (*((volatile unsigned long*) 0xE000ED9C))
#define MPU_RASR (*((volatile unsigned long*) 0xE000EDA0))
#define SCB_SHCSR (*((volatile unsigned long*) 0xE000ED24))
void Registers_Init(void)
{
//MPU Configuring
MPU_RNR = 0x00000000; //region is 0
MPU_RBAR = 0x20000000; //base address is 0x20000000
MPU_RASR = 0x1608FF0B; // enable bit=1, 64 bytes, no subregions, s=c=b=0, xn=1, permission=ro,ro
SCB_SHCSR |= 0x00010000; // enable MemManage Fault
MPU_CTRL = 0x00000005; // enable memory protection unit,guaranteeing default priviliged access
}
void MemManage_Handler(void)
{
__asm(
'MOV R4, 0x77777777\n\t'
'MOV R5, 0x77777777\n\t'
);
}
void HardFault_Handler(void)
{
__asm(
'MOV R4, 0x77777777\n\t'
'MOV R5, 0x77777777\n\t'
);
}
int main(void)
{
Registers_Init();
while(1)
{
__asm(
'LDR R0, =0x20000000\n\t'
'MOV R1, 0x77777777\n\t'
'STR R1, [R0,#0]'
);
}
return (1);
}
void SystemInit(void)
{
}
So, in main function, I am writing in restricted area i.e. 0x20000000, but MPU is not generating any fault and instead of calling MemManage_Handler()or HardFault_Handler(), it writes successfully.
Why is that? Please help.
The micro controller I am using is STM32F103RB.
#mpu #stm32f103rb #memory-protection #stm32 #cortex-m3
