Циклический(кольцевой) буфер.

#define RBUF_INIT(TYPE, LENPOW2 ) volatile struct { \
uint32_t wr; \
uint32_t rd; \
TYPE data[ 1 << (LENPOW2)]; \
}
 
#define RBUF_PUT( RBUF, YMM)  \
{ if((RBUF).rd == (RBUF).wr ) { \
(RBUF).wr = 0; \
(RBUF).rd = 0; \
} \
(RBUF).data[ RBUF_MASK(RBUF) & (RBUF).wr++] = YMM; }
 
#define RBUF_MASK(RBUF) ( sizeof((RBUF).data)/sizeof((RBUF).data[0]) -1)
#define RBUF_NOTEMPTY (RBUF) ((RBUF).rd < (RBUF).wr)
#define RBUF_NOTFULL (RBUF) ((RBUF).wr - (RBUF).rd <= RBUF_MASK(RBUF))
 
#define RBUF_GET( RBUF)  (RBUF).data[ RBUF_MASK(RBUF) & ((RBUF).rd++)];
 
//=========== ПРИМЕР ИСПОЛЬЗОВАНИЯ ========================
 
RBUF_INIT(uint8_t, 5) buf; //байтовый циклический буфер длинной 32
RBUF_INIT(Pack *, 3) packs; //циклический буфер пакетов длинной 8
 
void main(void)
{
if (RBUF_NOTEMPTY(buf)) uint8_t data = RBUF_GET(buf);
 
if (RBUF_NOTFULL(buf))RBUF_PUT(buf, 34);
 
}

if(!RBUF_NOTEMPTY(buf)){
 
}

#define RBUF_INIT(TYPE, LENPOW2 ) volatile struct { \
TYPE data[ 1 << (LENPOW2)]; \
TYPE *wr = data; \
TYPE *rd = data; \
}
 
#define RBUF_PUT( RBUF, YMM)  \
{ if((RBUF).rd == (RBUF).wr ) { \
(RBUF).wr = data; \
(RBUF).rd = data; \
} \
*(RBUF).data = YMM;  \
(RBUF).data++;}
 
#define RBUF_NOTEMPTY (RBUF) ((RBUF).rd < (RBUF).wr)
#define RBUF_NOTFULL (RBUF) ((RBUF).wr <  &(RBUF).data [1 << (LENPOW2)])
 
#define RBUF_GET( RBUF, DATA)  {(RBUF).rd++); \
DATA = *(RBUF).data; }