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Software flow control in console

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This adds software flow control handling (a.k.a X-on/X-off). When Ctrl-Q
is received, UART transmitting is paused until Ctrl-S is received. If
the FIFO or buffer fill up during this period, console output is lost.

BUG=chrome-os-partner:18680
TEST=Press Ctrl-Q and see console stopped. Press Ctrl-S and see buffered
messages.
BRANCH=spring

Change-Id: I9ce1198a1119dadc558bb522c48037bb83bba415
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/48887
Reviewed-by: Randall Spangler <rspangler@chromium.org>
This commit is contained in:
Vic Yang
2013-04-23 17:29:55 +08:00
committed by ChromeBot
parent 4d0c4b1a53
commit 2dd01e59ea
1 changed files with 17 additions and 2 deletions
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19
common/uart_buffering.c
View File

@@ -59,6 +59,7 @@ static volatile int rx_cur_buf_ptr;
static int last_rx_was_cr;
static int tx_snapshot_head;
static int tx_snapshot_tail;
static int uart_suspended;
static enum {
ESC_OUTSIDE, /* Not in escape code */
@@ -463,6 +464,13 @@ static void handle_console_char(int c)
history_next();
} else if (c == CTRL('P')) {
history_prev();
} else if (c == CTRL('Q')) {
uart_suspended = 1;
uart_tx_stop();
} else if (c == CTRL('S')) {
uart_suspended = 0;
if (uart_tx_stopped())
uart_tx_start();
} else if (c == '\n') { /* Newline */
uart_write_char('\r');
uart_write_char('\n');
@@ -500,6 +508,9 @@ void uart_process(void)
while (uart_rx_available())
handle_console_char(uart_read_char());
if (uart_suspended)
return;
/* Copy output from buffer until TX fifo full or output buffer empty */
fill_tx_fifo();
@@ -516,7 +527,7 @@ int uart_puts(const char *outstr)
break;
}
if (uart_tx_stopped())
if (!uart_suspended && uart_tx_stopped())
uart_tx_start();
/* Successful if we consumed all output */
@@ -527,7 +538,7 @@ int uart_vprintf(const char *format, va_list args)
{
int rv = vfnprintf(__tx_char, NULL, format, args);
if (uart_tx_stopped())
if (!uart_suspended && uart_tx_stopped())
uart_tx_start();
return rv;
@@ -546,6 +557,10 @@ int uart_printf(const char *format, ...)
void uart_flush_output(void)
{
/* If UART is suspended, ignore flush request. */
if (uart_suspended)
return;
/*
* If we're in interrupt context, copy output explicitly, since the
* UART interrupt may not be able to preempt this one.