I am looking for ideas for a receive buffer for a small application dealing with 15 byte packets at 921.6Kbaud over rs485. I am thinking of using a circular buffer as the interface between the UART ISR and main. As it is a microprocessor I was wanting to put
while (uartindex!=localindex) { do stuff }
in the
while (;;) {do forever}
part of main but I have been told this is not acceptable.
How do people deal with their uarts under similar circumstances?
ISR should fill a FIFO. Main should consume it.
Bellow a very simple fifo algorithm:
#define RINGFIFO_SIZE (1024) /* serial buffer in bytes (power 2) */
#define RINGFIFO_MASK (RINGFIFO_SIZE-1ul) /* buffer size mask */
/* Buffer read / write macros */
#define RINGFIFO_RESET(ringFifo) {ringFifo.rdIdx = ringFifo.wrIdx = 0;}
#define RINGFIFO_WR(ringFifo, dataIn) {ringFifo.data[RINGFIFO_MASK & ringFifo.wrIdx++] = (dataIn);}
#define RINGFIFO_RD(ringFifo, dataOut){ringFifo.rdIdx++; dataOut = ringFifo.data[RINGFIFO_MASK & (ringFifo.rdIdx-1)];}
#define RINGFIFO_EMPTY(ringFifo) (ringFifo.rdIdx == ringFifo.wrIdx)
#define RINGFIFO_FULL(ringFifo) ((RINGFIFO_MASK & ringFifo.rdIdx) == (RINGFIFO_MASK & (ringFifo.wrIdx+1)))
#define RINGFIFO_COUNT(ringFifo) (RINGFIFO_MASK & (ringFifo.wrIdx - ringFifo.rdIdx))
/* buffer type */
typedef struct{
uint32_t size;
uint32_t wrIdx;
uint32_t rdIdx;
uint8_t data[RINGFIFO_SIZE];
} RingFifo_t;
RingFifo_t gUartFifo;
(Care must be taken with this FIFO algorithm, size MUST be power of 2)
The ISR should behave like this:
void ISR_Handler()
{
uint8_t c;
while(UART_NotEmpty()) {
c = UART_GetByte();
RINGFIFO_WR(gUartFifo, c);
}
}
And the Main:
while(1)
{
if (!RINGFIFO_EMPTY(gUartFifo)) {
/* consume fifo using RINGFIFO_RD */
}
}
This algorithm reads the FIFO directly from the main loop, you should use a intermediate layer that checks if there is a full packet in the buffer, and deals with it, in such a manner that main would be like this:
uint8_t ptrToPacket;
uint32_t packetSize;
while(1)
{
if (!Uart_HasValidPacket()) {
Uart_GetPacket(&ptrToPacket, &packetSize)
/* Process packet using ptrToPacket and packetSize */
}
}