To check if it is a display error I would suggest to step into memcpy and see where the data
gets read from.
When using volatile, to get the compiler not to optimize the pointer value,
the volatile should be after the *. Before the * it means the value the pointer points to is volatile, and
as this code is not accessing it, it does not matter.
E.g.
const unsigned char * volatile src=(const unsigned char * volatile)(q->start);
I tried to simulate the queue_pop method with CW 4.7 and the code behaved properly as far as I
noticed. The src variable however was not shown in the debugger.
Please note which chip you are targeting and which tool versions you are using. I tried with a S12, the
OP might have problems with a S08 or something else. Don't forget to note the memory model or
anything else which might affect the setup.
Also when reducing the issue so far it is beneficial to go the last step and create a self contained, compilable sample showing the problem,
in this case the definition of the return type and some test values were all that was missing 
Daniel
#include <stdio.h>typedef struct{unsigned char pop_index; ///< Pop indexunsigned char push_index; ///< Push indexvoid *start; ///< Pointer to underlying storageunsigned char reclen; ///< Record sizeunsigned char used; ///< Number of entries usedunsigned char mask; ///< Mask of the number of records} queue_t;typedef enum { Q_EMPTY, Q_OK} queue_status_t; queue_status_t queue_pop(queue_t *q, void *p){ const unsigned char *src; if ( q->used == 0 ) { return Q_EMPTY; } if ( p != NULL ) { src=(const unsigned char *)(q->start) + ((q->pop_index & q->mask) * q->reclen); (void)memcpy(p, src, q->reclen); } q->pop_index++; q->used--; return Q_OK;}unsigned char buf[64] = { 0, 1,2,3,4,5,6,7,8,9};queue_t q = { 1,0, buf, 4, 1, 15};void main(void) { unsigned char buf2[4]; volatile queue_status_t r = queue_pop(&q, buf2);}
