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Subject[PATCH][2.4] serial.c xmit fifo overflow bug
Attached is a patch to correct a xmit fifo overflow bug in serial.c. I 
limited the changes to a patch and not a feature addition which would add
support for programming the tx fifo interrupt threshold.

I've tested it on an embedded system which uses an Exar ST16C654 QUART.


--- serial.c 2003/02/17 18:03:39 1.1
+++ serial.c 2003/02/18 16:30:11
@@ -698,7 +698,24 @@
return;
}

- count = info->xmit_fifo_size;
+ if (info->state->type == PORT_16654) {
+ /*
+ * The assumption in the following do loop is that the
+ * uart will interrupt when the number of bytes in the
+ * fifo drops to 0. The ST16654 will trigger the interrupt
+ * when the number of bytes drops below a programmed
+ * threshold. By default, the threshold is 8. There is no
+ * code in place in this driver to alter the transmit fifo
+ * threshold, so hard coding an 8 here is okay for now.
+ *
+ * This prevents overflowing the xmit fifo.
+ *
+ */
+ count = info->xmit_fifo_size - 8;
+ } else {
+ count = info->xmit_fifo_size;
+ }
+
do {
serial_out(info, UART_TX, info->xmit.buf[info->xmit.tail]);
info->xmit.tail = (info->xmit.tail + 1) & (SERIAL_XMIT_SIZE-1);
--

William King
Integrated Consulting, Inc.
William.King@dadaboom.com


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