在ARM Cortex-M0 +上调试硬故障（使用CMSIS DSP库）

Question

I'm using the CMSIS DSP library on a Cortex-M0+. Some functions, such as sqrt and FFT, are resulting in hard faults.

The arm_sqrt_f32 function calls sqrtf :

 arm_sqrt_f32(
 float32_t in,
 float32_t * pOut)
 [...]
 *pOut = sqrtf(in);

part of the generated code:

0x00003914:   bl 0x49e8 <sqrtf>
0x00003918:   adds r2, r0, #0
0x0000391a:   ldr r3, [r7, #0]
0x0000391c:   str r2, [r3, #0]

The hard fault happens on the str instruction at address 0x0000391c. When at this line, the registers are:

$r1 0x0 
$r2 0x40000000  
$r3 0x0 
$r4 0x0 
$r5 0x200017fc  
$r6 0x0 
$r7 0x200017e0  
$r8 0xfff7ffff  
$r9 0xefbffffe  
$r10    0xff7fffff  
$r11    0x0 
$r12    0x0 

the SP register is 0x200017e0, an address containing 0.

I can't figure out why I'm getting this hard fault. What should I do?

Thanks!

Answer 1

If the Cortex-M0 fault mechanism is the same as the Cortex-M3/4/7 fault mechanism, then the following page provides detailed information on how to decode the fault stack, giving you the address of the faulting instruction, as well as the register values at the time. http://www.freertos.org/Debugging-Hard-Faults-On-Cortex-M-Microcontrollers.html

Answer 2

Lets look at exactly what your str call is doing by looking at this page your str call is doing str r2,[r3, #0] which translates to (if i'm not mistaken) :

store r2 in the address r3 offset by #0

Looking at those register values, you are trying to put 0x40000000 into location 0x0 offset by 0, so 0x0 still. It is the equivalent of a segmentation fault, you are trying to access memory that is not avaliable to you thus causing the hard fault.

Seeing as how that code is generated, I'm assuming you are giving it a faulty pOut pointer.

Make sure you aren't calling the function by doing arm_sqrt_f32(float32_t foo, float32_t* pOut) , you'll want to call it by doing arm_sqrt_f32(float32_t foo, float32_t &pOut) where pOut may be delcared as float32_t pOut = bar; since, as a pointer arguement, its looking for an address