termios support

[Eric Norum]

Geoffroy Montel <g_montel at yahoo.com> wrote:
> But, wouldn't it be better if
> void rtems_termios_dequeue_characters (void *ttyp, int len)
> would be stg like
> int rtems_termios_dequeue_characters (void *ttyp, int len)
> and we'd return the state of the buffer ? (for instance, 0 when
> it's empty
> so that we stop the interrupts then, and 1 otherwise)
>

No, that would be redundant.

Have a look at the example write and transmit interrupt routines.   
I'll show them again since they're so short....

> =============================================================
> void
> device_write_routine (int minor, char *buf, int count)
> {
>         UART->output_register = *buf;
>         UART->control_register |= UART_TRANSMIT_INTERRUPT_ENABLE;
> }
>
> void
> device_transmit_interrupt_routine (int vector)
> {
>         UART->control_register &= ~UART_TRANSMIT_INTERRUPT_ENABLE;
>         rtems_termios_dequeue_characters (device_ttyp, 1);
> }
> =============================================================

Notice that the transmit interrupt service routine disables the  
transmit interrupt before calling rtems_termios_dequeue_characters().  


If the termios output buffer is empty,  
rtems_termios_dequeue_characters () just returns to the interrupt  
handler which returns and leaves the transmit interrupt disabled.

If the termios output buffer is not empty,  
rtems_termios_dequeue_characters() calls device_write_routine () to  
transmit the next character and reenable the transmit interrupt.  The  
device_write_routine returns to rtems_termios_dequeue_characters  
which in turn returns to the interrupt handler which returns and will  
again be invoked when the transmitter is ready.

---
Eric Norum                                 eric at skatter.usask.ca
Saskatchewan Accelerator Laboratory        Phone: (306) 966-6308
University of Saskatchewan                 FAX:   (306) 966-6058
Saskatoon, Canada.