[avr-gcc-list] Strange problem with UART

[Olav Torheim]

Finally I made my simple UART program work the way it should by leaving the read/write operations to interrupts routines. However, the main() function and the interrupts routines seemed not to be able to read/write the same variables, althought I suppose they should. To make the program work I had to force the variables UART_CHARACTER_RECEIVED and UART_READY to specific registers, then the main program and the interrupts finally would access the same data. Does anybody know why this is happening? Source code is attached below.

 

Olav Torheim

 

// Simple UART program returning received input as output:

 

#include <io.h>
#include <interrupt.h>
#include <signal.h>
#include <progmem.h>

#define UART_CPU               8000000      /* 4.00Mhz */
#define UART_BAUD_RATE         19200         /* baud rate*/
#define UART_BAUD_SELECT       (UART_CPU/(UART_BAUD_RATE*16l)-1)

register unsigned char UART_CHARACTER_RECEIVED asm("r3");
register unsigned char UART_READY asm("r4");

unsigned char   UART_RXCHAR;

SIGNAL(SIG_UART_RECV)
{
                UART_RXCHAR = inp(UDR);

                UART_CHARACTER_RECEIVED = 1;
}

// Interrupt-rutina som køyrer når yverføringi er avslutta:
SIGNAL(SIG_UART_TRANS)
{
        UART_READY = 1;
}

void UARTInit(void)
{
        // Initializing UART:
        outp(BV(RXCIE)|BV(TXCIE)|BV(RXEN)|BV(TXEN),UCSRB); // Setting the control register
  outp(UART_BAUD_SELECT, UBRR);  //Baudrate 19200
        sei(); // enabling global interrupts
        UART_READY = 1;
        UART_CHARACTER_RECEIVED = 0;
}

void UARTSend(char outchar)
{
                while(UART_READY != 1);
                UART_READY = 0;
                outp(outchar, UDR);
}

unsigned char UARTReceive(void)
{
        while(UART_CHARACTER_RECEIVED != 1);
        UART_CHARACTER_RECEIVED = 0;
        return inp(UART_RXCHAR);
}

int main(void)
{
        UARTInit();

  while(1)
         {
                UARTSend(UARTReceive());
         };
}

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