Rohit Grover / DumpRegistersAtHardFault

A hardfault handler to dump useful registers to aid debugging of program exceptions. Often knowing the ProgramCounter (PC) at fault time is enough to find a useful location in source code.

The library installs an alternate version of the HardFault_Handler to replace the system default. The replaced handler is able to emit useful registers on the system console to aid debugging. You can enhance the handler to emit more useful information.

How would one test this..

Here's how one might produce an exception to trigger a hard-fault. You would not want to do this in your project, but the snippet helps demonstrate the function of this library. The snippet comes from a shared project: PointerError.

// Example of hanging when reading a bad pointer
/* Refer to http://www.freertos.org/Debugging-Hard-Faults-On-Cortex-M-Microcontrollers.html */

#include "mbed.h"

DigitalOut myled(LED1);

unsigned x[10] = {0};

int main() {
    unsigned *ok_ptr = x;
    unsigned *bad_ptr = (unsigned*)0xe600b0; // not in RAM!
    printf("ok_ptr = 0x%08X, bad_ptr = 0x%08X\n", (unsigned)ok_ptr, (unsigned)bad_ptr);

    unsigned ok_read = ok_ptr[0];
    printf("ok_read = %d\n", ok_read);

    unsigned bad_read = bad_ptr[0];
    printf("bad_read = %d\n", bad_read);

    while(1) {
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}

Diff: hardfault.s

Revision:
1:c325619800b2
Parent:
0:68900ac9bc4b
--- a/hardfault.s	Wed Jan 29 15:27:24 2014 +0000
+++ b/hardfault.s	Wed Jan 29 18:47:15 2014 +0000
@@ -31,14 +31,4 @@
     ALIGN 4
 HANDLER2_ADDRESS_CONST DCD prvGetRegistersFromStack
 
-    END
-
-    ; call prvGetRegistersFromStack() with R0 set as the stack pointer at the
-    ; time of exception entry.
-    LDR R2, HANDLER2_ADDRESS_CONST
-    BX R2
-    IMPORT prvGetRegistersFromStack
-    ALIGN 4
-HANDLER2_ADDRESS_CONST DCD prvGetRegistersFromStack
-
-    END
+    END
\ No newline at end of file