g: tweak cflush() to wait a bit longer

It turns out that even when the UART status register returns TX_IDLE
bit set, the transmitter is still active - probably working out the
stop sequence.

So, resetting immediately after TX_EMPTY is asserted causes the last
character to be corrupted on the receiving side.

This patch adds a wait for the duration of transmitting 10 bits at
115200 baud, which should be plenty. Wait loop in capped in case timer
is not running for any reason.

BRANCH=none
BUG=chrome-os-partner:60321
TEST=added code to print out a string and then call cflush() and reset
     immediately. The last character is not lost any more, the exact
     string is printed.

Change-Id: If386c515d9d9cc63d161fba73e6ed4e70e465136
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/418487
Reviewed-by: Mary Ruthven <mruthven@chromium.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/chip/g/uartn.c b/chip/g/uartn.c
index c6c80ced51..2de44ab208 100644
--- a/chip/g/uartn.c
+++ b/chip/g/uartn.c
@@ -68,9 +68,22 @@ int uartn_tx_in_progress(int uart)
 
 void uartn_tx_flush(int uart)
 {
+	timestamp_t ts;
+	int i;
+
 	/* Wait until TX FIFO is idle. */
 	while (uartn_tx_in_progress(uart))
 		;
+	/*
+	 * Even when uartn_tx_in_progress() returns false, the chip seems to
+	 * be still trasmitting, resetting at this point results in an eaten
+	 * last symbol. Let's just wait some time (required to transmit 10
+	 * bits at 115200 baud).
+	 */
+	ts = get_time(); /* Start time. */
+	for (i = 0; i < 1000; i++) /* Limit it in case timer is not running. */
+		if ((get_time().val - ts.val) > ((1000000 * 10) / 115200))
+			return;
 }
 
 int uartn_tx_ready(int uart)