[PATCH] rtems_termios_puts: Copy and write more than one char at once
Joel Sherrill
joel.sherrill at oarcorp.com
Mon Aug 18 23:41:36 UTC 2014
I committed this. Thanks.
If there is something I missed, please let me know.
--joel
On 8/14/2014 10:02 AM, Kolja Waschk wrote:
> Renamed startXmit(), nToSend is unsigned, just check FL_ORCVXOF, no (void) cast anymore, compute nToSend in single if/else if/else.
>
>
> ---
> cpukit/libcsupport/src/termios.c | 135 ++++++++++++++++++++++++---------------
> 1 file changed, 85 insertions(+), 50 deletions(-)
>
> diff --git a/cpukit/libcsupport/src/termios.c b/cpukit/libcsupport/src/termios.c
> index 2448ea1..216834c 100644
> --- a/cpukit/libcsupport/src/termios.c
> +++ b/cpukit/libcsupport/src/termios.c
> @@ -974,6 +974,49 @@ rtems_termios_ioctl (void *arg)
> }
>
> /*
> + * Send as many chars at once as possible to device-specific code.
> + * If transmitting==true then assume transmission is already running and
> + * an explicit write(0) is needed if output has to stop for flow control.
> + */
> +static unsigned int
> +startXmit (
> + struct rtems_termios_tty *tty,
> + unsigned int newTail,
> + bool transmitting
> +)
> +{
> + unsigned int nToSend;
> +
> + tty->rawOutBufState = rob_busy;
> +
> + /* if XOFF was received, do not (re)start output */
> + if (tty->flow_ctrl & FL_ORCVXOF) {
> + /* set flag, that output has been stopped */
> + tty->flow_ctrl |= FL_OSTOP;
> + nToSend = 0;
> + /* stop transmitter */
> + if (transmitting) {
> + (*tty->handler.write) (tty, NULL, 0);
> + }
> + } else {
> + /* when flow control XON or XOF, don't send blocks of data */
> + /* to allow fast reaction on incoming flow ctrl and low latency*/
> + /* for outgoing flow control */
> + if (tty->flow_ctrl & (FL_MDXON | FL_MDXOF))
> + nToSend = 1;
> + else if (newTail > tty->rawOutBuf.Head)
> + nToSend = tty->rawOutBuf.Size - newTail;
> + else
> + nToSend = tty->rawOutBuf.Head - newTail;
> +
> + (*tty->handler.write)(
> + tty, &tty->rawOutBuf.theBuf[newTail], nToSend);
> + }
> +
> + return nToSend;
> +}
> +
> +/*
> * Send characters to device-specific code
> */
> void
> @@ -989,21 +1032,16 @@ rtems_termios_puts (
> (*tty->handler.write)(tty, buf, len);
> return;
> }
> - newHead = tty->rawOutBuf.Head;
> +
> while (len) {
> - /*
> - * Performance improvement could be made here.
> - * Copy multiple bytes to raw buffer:
> - * if (len > 1) && (space to buffer end, or tail > 1)
> - * ncopy = MIN (len, space to buffer end or tail)
> - * memcpy (raw buffer, buf, ncopy)
> - * buf += ncopy
> - * len -= ncopy
> - *
> - * To minimize latency, the memcpy should be done
> - * with interrupts enabled.
> - */
> - newHead = (newHead + 1) % tty->rawOutBuf.Size;
> + size_t nToCopy;
> + size_t nAvail;
> +
> + /* Check space for at least one char */
> + newHead = tty->rawOutBuf.Head + 1;
> + if (newHead >= tty->rawOutBuf.Size)
> + newHead -= tty->rawOutBuf.Size;
> +
> rtems_termios_interrupt_lock_acquire (tty, &lock_context);
> while (newHead == tty->rawOutBuf.Tail) {
> tty->rawOutBufState = rob_wait;
> @@ -1014,21 +1052,41 @@ rtems_termios_puts (
> rtems_fatal_error_occurred (sc);
> rtems_termios_interrupt_lock_acquire (tty, &lock_context);
> }
> - tty->rawOutBuf.theBuf[tty->rawOutBuf.Head] = *buf++;
> +
> + /* Determine free space up to current tail or end of ring buffer */
> + nToCopy = len;
> + if (tty->rawOutBuf.Tail > tty->rawOutBuf.Head) {
> + /* Available space is contiguous from Head to Tail */
> + nAvail = tty->rawOutBuf.Tail - tty->rawOutBuf.Head - 1;
> + } else {
> + /* Available space wraps at buffer end. To keep it simple, utilize
> + only the free space from Head to end during this iteration */
> + nAvail = tty->rawOutBuf.Size - tty->rawOutBuf.Head;
> + /* Head may not touch Tail after wraparound */
> + if (tty->rawOutBuf.Tail == 0)
> + nAvail--;
> + }
> + if (nToCopy > nAvail)
> + nToCopy = nAvail;
> +
> + /* To minimize latency, the memcpy could be done
> + * with interrupts enabled or with limit on nToCopy (TBD)
> + */
> + memcpy(&tty->rawOutBuf.theBuf[tty->rawOutBuf.Head], buf, nToCopy);
> +
> + newHead = tty->rawOutBuf.Head + nToCopy;
> + if (newHead >= tty->rawOutBuf.Size)
> + newHead -= tty->rawOutBuf.Size;
> tty->rawOutBuf.Head = newHead;
> +
> if (tty->rawOutBufState == rob_idle) {
> - /* check, whether XOFF has been received */
> - if (!(tty->flow_ctrl & FL_ORCVXOF)) {
> - (*tty->handler.write)(
> - tty, &tty->rawOutBuf.theBuf[tty->rawOutBuf.Tail],1);
> - } else {
> - /* remember that output has been stopped due to flow ctrl*/
> - tty->flow_ctrl |= FL_OSTOP;
> - }
> - tty->rawOutBufState = rob_busy;
> + startXmit (tty, tty->rawOutBuf.Tail, false);
> }
> +
> rtems_termios_interrupt_lock_release (tty, &lock_context);
> - len--;
> +
> + buf += nToCopy;
> + len -= nToCopy;
> }
> }
>
> @@ -1678,35 +1736,12 @@ rtems_termios_refill_transmitter (struct rtems_termios_tty *tty)
> if ( tty->tty_snd.sw_pfn != NULL) {
> (*tty->tty_snd.sw_pfn)(&tty->termios, tty->tty_snd.sw_arg);
> }
> - }
> - /* check, whether output should stop due to received XOFF */
> - else if ((tty->flow_ctrl & (FL_MDXON | FL_ORCVXOF))
> - == (FL_MDXON | FL_ORCVXOF)) {
> - /* Buffer not empty, but output stops due to XOFF */
> - /* set flag, that output has been stopped */
> - tty->flow_ctrl |= FL_OSTOP;
> - tty->rawOutBufState = rob_busy; /*apm*/
> - (*tty->handler.write) (tty, NULL, 0);
> - nToSend = 0;
> } else {
> /*
> - * Buffer not empty, start tranmitter
> + * Buffer not empty, check flow control, start transmitter
> */
> - if (newTail > tty->rawOutBuf.Head)
> - nToSend = tty->rawOutBuf.Size - newTail;
> - else
> - nToSend = tty->rawOutBuf.Head - newTail;
> - /* when flow control XON or XOF, don't send blocks of data */
> - /* to allow fast reaction on incoming flow ctrl and low latency*/
> - /* for outgoing flow control */
> - if (tty->flow_ctrl & (FL_MDXON | FL_MDXOF)) {
> - nToSend = 1;
> - }
> - tty->rawOutBufState = rob_busy; /*apm*/
> - (*tty->handler.write)(
> - tty, &tty->rawOutBuf.theBuf[newTail], nToSend);
> + nToSend = startXmit (tty, newTail, true);
> }
> - tty->rawOutBuf.Tail = newTail; /*apm*/
> }
>
> rtems_termios_interrupt_lock_release (tty, &lock_context);
--
Joel Sherrill, Ph.D. Director of Research & Development
joel.sherrill at OARcorp.com On-Line Applications Research
Ask me about RTEMS: a free RTOS Huntsville AL 35805
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