Re: [avr-gcc-list] interrupt-driven buffered UART receiver

[Lorne Gutz]

 Michael sorry about that, and thanks for pointing it out

   In the code that works things are a little different.
See below.

Lorne

On Tuesday 11 March 2003 16:07, Michael Jin wrote:
> Lorne Gutz wrote:
> > On Tuesday 11 March 2003 06:20, Olaf Zenker wrote:
> >> address@hidden
> >
> > Hi folks,
> >
> >      To date I have not seen any driver written in C.
> >
> > I will send some that I have used in the past.   This
> > code has been written to produce small code, and
> > should be compiled with -Os.
> >
> > cheers
> > Lorne
>
> [snip]
>
> > // UART Transmitter buffer
> > static uint8_t      tx_buff[16];
> > static uint8_t      tx_wr_index,tx_rd_index;
> > volatile uint8_t    tx_counter;
> >
> > // UART Transmitter interrupt service routine
> > SIGNAL( SIG_UART_DATA )
> > {
> >     uint8_t     tx_buffer_size = 16;
> >
> >     if( tx_counter != 0 ){
> >         tx_counter--;
> >
> >         tx_wr_index++;
> >         if( tx_wr_index > tx_buffer_size )
> >             tx_wr_index = 0;
> >
> >         outp( tx_buff[ tx_wr_index ], UDR );
> >
> >     }
> > }
> >
> >
> > // Write a character to the UART Transmitter buffer
> >
> > void    putchar( uint8_t c )
> > {
> >     uint8_t     tx_buffer_size = 16;
> >
> >     while( tx_counter >= tx_buffer_size );
> >
> >     if( ( tx_counter == 0 ) && ( bit_is_clear( USR, UDRE )))
> >         outp( c, UDR );
> >
> >     else{
> >
> >         tx_counter++;
The above line should be
             tx_rd_index++;
I'm impressed that you found an error like that.

> >         if( tx_rd_index >= tx_buffer_size )
> >             tx_rd_index = 0;
> >
> >         tx_buff[ tx_rd_index ] = c;
> >
> >         cli();
> >         tx_counter++;
> >         sei();
> >     }
> > }
>
> I don't quite understand this piece of code, can you explain why the
> tx_rd_index never increased while the tx_counter did twice in the above
> function please?
> TIA.
>
> Michael