[avr-gcc-list] UART again

[Carsten Scharfenberg]

Hi,
last month Ron submitted code for a buffered UART transmitter based upon TX 
Complete Interrupt which arose the question of using the Data Register Empty 
Interrupt. - So I did, but whenever I enable UDRIE in UCR no UART interrupts 
seem to be triggered.
Here's a sample code of mine which uses three interrupts - everyone switching 
another led on and off when being called: SIG_UART_TRANS for showing if any 
TXC interrupts are triggered, SIG_UART_DATA for showing if any UDRE 
interrupts are triggered and SIG_OVERFLOW0 for showing if the whole 
controller is working as it should.

#include <io.h>
#include <interrupt.h>
#include <sig-avr.h>

void init();


int main()
{
    init();
    outp( 0, UDR );
    
    for(;;);
    
    return 0;
}


INTERRUPT( SIG_OVERFLOW0 )
{
    static led = 0;
    
    if( led & 1 )
        sbi( PORTB, 7 );
    else
        cbi( PORTB, 7 );
    
    led++;
}

INTERRUPT( SIG_UART_TRANS )
{
    static led = 0;
    
    if( led & 1 )
        sbi( PORTB, 0 );
    else
        cbi( PORTB, 0 );
    
    outp( 0, UDR );
    
    led++;
}

INTERRUPT( SIG_UART_DATA )
{
    static led = 0;
    
    if( led & 1 )
        sbi( PORTB, 1 );
    else
        cbi( PORTB, 1 );
    
    outp( 0, UDR );
    
    led++;
}

void init()
{
    /******* UART Setup Code ****/
    outp( 0x26, UBRR );
    outp( 0x68, UCR );
    
    /******* Port B Setup Code ****/
    outp( 0xff, DDRB );
    outp( 0xff, PORTB );
    
    /******* Timer0 Setup Code ****/
    outp( 0x07, TCCR0 );
    outp( 0x00, TCNT0 );
    outp( 0x01, TIMSK );
     
    /******* Enable All Interrupts ****/
    sei();
}

This is the result:
if enable only the TXC interrupt, everything works fine. If I enable the UDRE 
interrupt whithout having a corresponding interrupt service routine only the 
timer led is blinking - no matter if TXC is also enabled. And if I enable 
UDRE while having a corresponding interrupt service routine (as shown above) 
nothing happens - all leds are dead.
why this?
I haven't had any problems like these when I wrote such code in Assembler 
with AVR-Studio.

Carsten