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Hard Fault in cortex m4

hemant

Hello All,

Good Morning!

I am working on Cortex m4.

I have read following about hard fault ,

"Bus Fault: detects memory access errors on instruction fetch, data read/write, interrupt vector fetch, and register stacking (save/restore) on interrupt (entry/exit)

Memory Management Fault: detects memory access violations to regions that are defined in the Memory Management Unit (MPU); for example code execution from a memory region with read/write access only.

Usage Fault: detects execution of undefined instructions, unaligned memory access for load/store multiple. When enabled, divide-by-zero and other unaligned memory accesses are also detected. Hard Fault: is caused by Bus Fault, Memory Management Fault, or Usage Fault if their handler cannot be executed"

Can anyone please explain with examples about Bus, Memory, Usage fault?

Can you please share any good links to read more about them in reference with ARM cortex m4 architecture?

Further, I have following code written in C running on cortex m4,

typedef struct {

  uint32_t nodeId;

  uint32_t systemId;

  int8_t serialNumber[16];

}sysConfig_t;

typedef struct {

  pktHeader_t pktHeader;

  uint8_t data[120];

}packet_t;

void *data;     //(this is pointer to array, i don't know exact alignment of this array )

packet_t *pkt = (uint8_t *)data;

sysConfig_t *sysData;

sysData = (sysConfig_t *)pkt->data;

printf(" %d %d ",sysData->nodeId, sysData->systemId);

I am getting Hard fault at printf statement. Why?

Can you please help?

According to me cortex m4 is based on arm v6 which supports handling unaligned addresses.

Can we discuss?

Thanks for reading my post.

Thanks

Hemant Undale.

Parents
  • +1 in reply to Simon Craske

    Hello Simon,

    thank you for your information.

    It is very helpful for me (I am not the original poster).

    At GCC, to add 'packed' attribute to the struct is "__attribute__((__packed__))".

    Therefore

    typedef __packed struct {  
 uint64_t value;  
} safe_t;

    should be the following.

    typedef struct {  
 uint64_t value;  
} __attribute__((__packed__)) safe_t;

    This is just F.Y.I.

    Also I verified your statement by the next code.

    typedef struct {  
  uint64_t value;  
}  unsafe_t; 
uint64_t func1(unsafe_t *p)  
{  
  return p->value; // Likely produces LDRD  
} 

typedef struct {  
 uint64_t value;  
} __attribute__((__packed__)) safe_t; 
uint64_t func2(safe_t *p)  
{  
  return p->value; // Likely produces 2x LDR  
}

    The generated source code is below.

    func1:
        ldrd    r0, [r0]
        bx      lr
func2:
        mov    r3, r0
        ldr    r0, [r0]        @ unaligned
        ldr    r1, [r3, #4]    @ unaligned
        bx      lr

    Best regards,

    Yasuhiko Koumoto.

Reply
  • +1 in reply to Simon Craske

    Hello Simon,

    thank you for your information.

    It is very helpful for me (I am not the original poster).

    At GCC, to add 'packed' attribute to the struct is "__attribute__((__packed__))".

    Therefore

    typedef __packed struct {  
 uint64_t value;  
} safe_t;

    should be the following.

    typedef struct {  
 uint64_t value;  
} __attribute__((__packed__)) safe_t;

    This is just F.Y.I.

    Also I verified your statement by the next code.

    typedef struct {  
  uint64_t value;  
}  unsafe_t; 
uint64_t func1(unsafe_t *p)  
{  
  return p->value; // Likely produces LDRD  
} 

typedef struct {  
 uint64_t value;  
} __attribute__((__packed__)) safe_t; 
uint64_t func2(safe_t *p)  
{  
  return p->value; // Likely produces 2x LDR  
}

    The generated source code is below.

    func1:
        ldrd    r0, [r0]
        bx      lr
func2:
        mov    r3, r0
        ldr    r0, [r0]        @ unaligned
        ldr    r1, [r3, #4]    @ unaligned
        bx      lr

    Best regards,

    Yasuhiko Koumoto.

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