Hard Fault Handler

RE: Hard Fault Handler

Sai Kiran — Tue, 11 Feb 2020 09:14:37 GMT

Thanks Bill. Will try doing whatever you told.

RE: Hard Fault Handler

wpaul — Mon, 10 Feb 2020 18:56:26 GMT

That's probably not the exact instruction that triggered the fault. More likely that's the first instruction of the hardfault handler at address 0xa60.

You are trying to store a 64-bit value to an address pointed to by a char * pointer. You shouldn't do that. You're forcing the compiler to do it with casts. But to store a 64-bit quantity to RAM, the compiler will generate an STRD (STorRe Doubleword) instruction. And there is a restriction with the Cortex-M4 processor that LDRD/STRD instructions can't be misaligned:

https://developer.arm.com/docs/dui0553/a/the-cortex-m4-instruction-set/about-the-instruction-descriptions/address-alignment

Note that according to the documentation above, full word loads and stores (LDR/STR) and halfword loads and stores (LDRH/STRH) can handle unaligned accesses, but double-word loads/store can not.

So if you really need to store the a 64-bit value in your char * array, you have two choices:

1) Allocate your char * array "c" such that it always starts on an 8-byte aligned address

2) use a memcpy() to copy the 64-bit value from tmp to the array.

Oh, also, the reason you're getting a HardFault instead of a UsageFault is that you probably don't have a UsageFault handler installed. There is also a SCB->SHCSR register where you can specifically enable usage fault, bus fault and memory manager faults. If you don't, all of those things will just trigger as a hard fault.

-Bill

RE: Hard Fault Handler

Sai Kiran — Mon, 10 Feb 2020 14:59:10 GMT

In the disassembler, here is the exact instruction: ldr r3, [PC, #4]. PC = 0x00000a60. I am not quite clear on what you mean by checking char* pointer arguments. Should I check that the values these pointers hold are word-aligned? I have checked the value of 'c' in the code. It stores the address where the resultant cipher text has to be placed. It's value is 0x20003cd7. So it is not dividable by 4. How do I change that?

RE: Hard Fault Handler

Turbo J — Mon, 10 Feb 2020 09:46:38 GMT

Check disassembly: The compiler probably generated some "LDRD" or "STRD" instructions.

These will FAULT on non-word alinged addresses. Check all of the char* pointer arguments - if these are not word-aligned (address dividable by 4), this will cause faults.