FIFO buffer in C for AT89s8252

Anyone help with this, not very good at C yet. What I have is an AT89s8252 programmed with k**l and tiny rtos. I have one task that that sits and uses _getkey and assigns it to an 8 bit int global variable. This variable is then read by another task that processes it if > 0. The problem I have is that if more than one number is received in a period less than the processing time, I find I am missing it. What I would like to do is for the _getkey task to write to a buffer of 10 say, and then read it in the other task, of course when a particular location is read it should then be destroyed and the next in the queue move up to be processed, until the buffer was empty. I have searched on the web, but cannot find anything suitable for MCUs. I had thought that this chip had a hardware buffer, but in this application it seems to have no effect. Would very much appreciate any assistance on this.

Mike

fifo in c

I usually do something like these code fragments:

c fifo

Brilliant, just what I was looking for. It is similar to what I was trying to do, but I guess I screwed up in a few places, I can see where now. Many thanks.

c fifo buffer

There is another little trik with FIFO buffers.

If you use good FIFO sizes (16, 32, 64 or 128 bytes) you can use >> operator instead %.

But if you use 256 bytes FIFO size and one byte FIFO buffer pointer you don't need any divide operator, only pointer increment operation.

#define FIFO_BUFFER_SIZE 256

unsigned char FIFO[FIFO_BUFFER_SIZE];
unsigned char BUFFER[2048];

unisgned char *pw, *pr; // use appropriate compiler directive for one byte pointers
unisgned char *p; // two-byte pointer

void interrupt_service_routine()
{
*pw++=get_input_byte();
}

void main() {
pw=&FIFO[0]; // Init FIFO write pointer
pr=&FIFO[0]; // Init FIFO read pointer

p=&BUFFER[0];


// In some process routine check state of FIFO and store received bytes to
// linear buffer.

while (pr!= pw) {
*p++=*pr++; // store received byte
}

// In another process routine check, process and empty BUFFER

if (p!=BUFFER[0]) {
check_buffer();
if (condition_to_empty_buffer) {
p=BUFFER[0];
}
}
}