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uart_ow: prevent possible infinite loop in _ow_read_byte()

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With a broken device, or a broken interface circuit, it is possible
for _ow_read_byte() to spin forever.  This patch arranges for it to
timeout after 5 seconds if it cannot read a valid byte from the UART.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
This commit is contained in:
Jon Trulson
2017-03-13 13:32:01 -06:00
committed by Brendan Le Foll
parent c7a4a6db34
commit f6f124a35f
1 changed files with 18 additions and 5 deletions
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23
src/uart_ow/uart_ow.c
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@@ -35,7 +35,7 @@
#include <termios.h>
#include <fcntl.h>
#include <errno.h>
#include <time.h>
#include "uart.h"
#include "uart_ow.h"
#include "mraa_internal.h"
@@ -44,10 +44,21 @@
static mraa_result_t
_ow_read_byte(mraa_uart_ow_context dev, uint8_t *ch)
{
while (!mraa_uart_read(dev->uart, (char*) ch, 1))
;
time_t thetime = time(NULL);
// add 5 seconds -- our crude timeout
thetime += 5;
return MRAA_SUCCESS;
int rv;
do {
rv = mraa_uart_read(dev->uart, (char*) ch, 1);
} while (rv == 0 && (time(NULL) < thetime));
if (rv == 0) {
return MRAA_ERROR_NO_DATA_AVAILABLE; // we timed out
}
else {
return MRAA_SUCCESS;
}
}
// low-level write byte
@@ -402,7 +413,9 @@ mraa_uart_ow_reset(mraa_uart_ow_context dev)
/* pull the data line low */
_ow_write_byte(dev, 0xf0);
_ow_read_byte(dev, &rv);
if (_ow_read_byte(dev, &rv) != MRAA_SUCCESS) {
return MRAA_ERROR_NO_DATA_AVAILABLE;
}
/* back up to high speed for normal data transmissions */
if (_ow_set_speed(dev, 1) != MRAA_SUCCESS) {