Fix from Eric Norum <eric@skatter.usask.ca>:

"Thomas Doerfler" <td@imd.m.isar.de> wrote:
>
> While implementing/testing the console/termios support for
> PPC403 in RTEMS-4.0.0-beta3, I am stuck at a certain location in
> termios.c:
>
> During "rtems_termios_initialize", the main control data structure
> "*tty" is allocated using malloc(). (Note, that malloc does not
> clear the allocated memory and my BSP does not clear memory during
> startup). Furtheron, a lot of fields of that structure are
> initialized, but the field "rawOutBufState" is not, and therefore
> keeps an arbitrary contents.
>
> When "osend()" is called the first time(with the serial device
> driver working in interrupt mode), termios gets stuck and will not
> call the device drivers output function.
>
> My questions now are:
>
> - anybody already experienced this bug?
> - is it a bug at all or did I do anything fundamentally wrong?
> - is there already a common bugfix for that?
>
> I don't like poking around in other people code, as long as I am
> not absolutely sure, what I do...

Yes, there's a bug there.
I thought that Joel had patched this already, but here's a patch to
fix this.  This patch also addresses a concern that many others have
raised regarding enabling and disabling of transmitter interrupts.

First, here's the example I've been using of a simple UART-style
interrupt-driven driver:
===============================================================
void
device_write_routine (int minor, char *buf, int count)
{
        UART->control_register &= ~UART_TRANSMITTER_READY;
        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);
}
==============================================================


Several people have expressed their concern about the disable/enable
of transmitter interrupts for every character.  On some machines
this disable/enable is an expensive operation.  With the attached
patch applied you can write the two routines as:
==============================================================
void
device_write_routine (int minor, char *buf, int count)
{
        code_to_clear_transmitter_ready_status ();
        if (device_ttyp->rawOutBufState == rob_idle)
                code_to_enable_transmitter_interrupts ();
        code_to_send_one_character_to_transmitter (*buf);
}

void
device_transmit_interrupt_routine (int vector)
{
        rtems_termios_dequeue_characters (device_ttyp, 1);
        if (device_ttyp->rawOutBufState == rob_idle)
                code_to_disable_transmitter_interrupts ();
}
===============================================================

0 files changed, 0 insertions, 0 deletions