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[avr-gcc-list] Probably a bug

From: Shahpour Moavenat
Subject: [avr-gcc-list] Probably a bug
Date: Tue, 8 Jun 2004 10:10:58 -0700 (PDT)

Hi all,

Below the email is the source file which problem occurs in.
The problem is in function putchar1, the while loop is translated to

while (tx_counter1 == TX_BUFFER_SIZE1); 
from .lst file:
153                     .LM12:
 154 006a 8091 0000             lds r24,tx_counter1
 155                    .L5:
 156 006e 8830                  cpi r24,lo8(8)
 157 0070 F1F3                  breq .L5

which is a never ending loop when tx_counter1 equals TX_BUFFER_SIZE1. But
in the main program if a SIG_UART1_TRANS interrupt occurs the tx_counter1
decrements one and the while loop in putchar1 should end. But the
generated assembly code, does not see this change (it only sees the
register value not the variable value).

I'm not sure if it is bug or not. But at least, it seems in some
situations the generated assembly code does not do what is meant by the
written C code.

I  work in WinAVR 20040404 under Windows XP.

Thank you,
S. Moavenat

The source code:
#include <avr/io.h>     
#include <avr/signal.h>
#include <avr/interrupt.h>
#include <avr/sfr_defs.h>

void putchar1(char c);


// USART1 Transmitter buffer
#define TX_BUFFER_SIZE1 8
char tx_buffer1[TX_BUFFER_SIZE1];
unsigned char tx_wr_index1,tx_rd_index1,tx_counter1;

// USART1 Transmitter interrupt service routine
//interrupt [USART1_TXC] void uart1_tx_isr(void)
if (tx_counter1)
   if (tx_rd_index1 == TX_BUFFER_SIZE1) tx_rd_index1=0;

// Write a character to the USART1 Transmitter buffer
void putchar1(char c)
while (tx_counter1 == TX_BUFFER_SIZE1);
//if(tx_counter1 == TX_BUFFER_SIZE1) return;
if (tx_counter1 || ((UCSR1A & DATA_REGISTER_EMPTY)==0))
   if (tx_wr_index1 == TX_BUFFER_SIZE1) tx_wr_index1=0;
else UDR1=c;
// Declare your global variables here
int main(void)

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