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 ();
}
===============================================================

1 files changed, 2 insertions, 14 deletions

diff --git a/c/src/exec/libcsupport/src/termios.c b/c/src/exec/libcsupport/src/termios.c
index e7fcf8ee30..f6b5652e57 100644
--- a/c/src/exec/libcsupport/src/termios.c
+++ b/c/src/exec/libcsupport/src/termios.c
@@ -213,7 +213,6 @@ rtems_termios_open (
 		}
 		tty->forw = ttyHead;
 		ttyHead = tty;
-		tty->back = NULL;
 		if (ttyTail == NULL)
 			ttyTail = tty;
 
@@ -247,9 +246,6 @@ rtems_termios_open (
 			&tty->rawOutBufSemaphore);
 		if (sc != RTEMS_SUCCESSFUL)
 			rtems_fatal_error_occurred (sc);
-		tty->rawOutBufHead = 0;
-		tty->rawOutBufTail = 0;
-		tty->refcount = 0;
 		tty->rawOutBufState = rob_idle;
 
 		/*
@@ -265,17 +261,9 @@ rtems_termios_open (
 				&tty->rawInBufSemaphore);
 			if (sc != RTEMS_SUCCESSFUL)
 				rtems_fatal_error_occurred (sc);
-			tty->rawInBufHead = 0;
-			tty->rawInBufTail = 0;
 		}
 
 		/*
-		 * Initialize variables
-		 */
-		tty->column = 0;
-		tty->cindex = tty->ccount = 0;
-
-		/*
 		 * Set default parameters
 		 */
 		tty->termios.c_iflag = BRKINT | ICRNL | IXON | IMAXBEL;
@@ -481,9 +469,9 @@ osend (const char *buf, int len, struct rtems_termios_tty *tty)
 		tty->rawOutBuf[tty->rawOutBufHead] = *buf++;
 		tty->rawOutBufHead = newHead;
 		if (tty->rawOutBufState == rob_idle) {
-			tty->rawOutBufState = rob_busy;
 			(*tty->device.write)(tty->minor,
 				(char *)&tty->rawOutBuf[tty->rawOutBufTail], 1);
+			tty->rawOutBufState = rob_busy;
 		}
 		rtems_interrupt_enable (level);
 		len--;
@@ -935,12 +923,12 @@ rtems_termios_dequeue_characters (void *ttyp, int len)
 		/*
 		 * Buffer not empty, start tranmitter
 		 */
-		tty->rawOutBufState = rob_busy;
 		if (newTail > tty->rawOutBufHead)
 			nToSend = RAW_OUTPUT_BUFFER_SIZE - newTail;
 		else
 			nToSend = tty->rawOutBufHead - newTail;
 		(*tty->device.write)(tty->minor, (char *)&tty->rawOutBuf[newTail], nToSend);
+		tty->rawOutBufState = rob_busy;
 	}
 	tty->rawOutBufTail = newTail;
 }