Hello, I struggle with the M3 DCSM unlock sequence...
What I would like to do is reset the security to a clean state with CSM-ARMED (bit-11) being set.
I try to get to this state by first setting the FORCESEC bit, and then performing a dummy read to the password locations. This seems to work when performed using the JTAG emulator, but when I run the same sequence from non-secure RAM in the MCU, I cannot get the CSM to arm. Below is the test code and debug output. I must be missing something fundamental.
Unfortunately, the Technical Reference is very vague on the DCSM topic.
Is there another application note, or possibly some sample code that you could share with me?
Thank you!
Debug terminal:
CSM status before forcesec: 0x00001F80 CSM status after forcesec: 0x00000460 OTPSECLOCK: 0x00FFFFFF CSM status after OTPSECLOCK read : 0x00000460 CSM status after password read : 0x00000440
Code:
volatile unsigned long status, temp;
// disable Protection
HWREG(SYSCTL_MWRALLOW) = 0xA5A5A5A5;
status = HWREG(CSM_BASE + DCSM_O_Z1_CR);
DEBUG_WRITE_STRING("CSM status before forcesec: 0x");
DEBUG_WRITE_LONG(status);
DEBUG_WRITE_STRING("\n\r");
// start clean
HWREG(CSM_BASE + DCSM_O_Z1_CR) |= DCSM_CR_FORCESEC; // FORCESEC = 1
status = HWREG(CSM_BASE + DCSM_O_Z1_CR);
DEBUG_WRITE_STRING("CSM status after forcesec: 0x");
DEBUG_WRITE_LONG(status);
DEBUG_WRITE_STRING("\n\r");
status = HWREG(0x680800); // OTPSECLOCK in OPT
status = HWREG(CSM_BASE + 0x120); // OTPSECLOCK register
DEBUG_WRITE_STRING("OTPSECLOCK: 0x");
DEBUG_WRITE_LONG(status);
DEBUG_WRITE_STRING("\n\r");
status = HWREG(CSM_BASE + DCSM_O_Z1_CR);
DEBUG_WRITE_STRING("CSM status after OTPSECLOCK read : 0x");
DEBUG_WRITE_LONG(status);
DEBUG_WRITE_STRING("\n\r");
temp = HWREG(FLASH_BASE + ZONE1_CSMPSWD0_OFFSET);
temp = HWREG(FLASH_BASE + ZONE1_CSMPSWD1_OFFSET);
temp = HWREG(FLASH_BASE + ZONE1_CSMPSWD2_OFFSET);
temp = HWREG(FLASH_BASE + ZONE1_CSMPSWD3_OFFSET);
status = HWREG(CSM_BASE + DCSM_O_Z1_CR);
DEBUG_WRITE_STRING("CSM status after password read : 0x");
DEBUG_WRITE_LONG(status);
DEBUG_WRITE_STRING("\n\r");
