Add cancellation support to several backends.

Some backends are technically capable of supporting cancellation, but
still lacked the necessary code to enable it.

src/cressi_edy.c

@@ -83,6 +83,9 @@ cressi_edy_transfer (cressi_edy_device_t *device, const unsigned char command[],
 
 	assert (asize >= csize);
 
+	if (device_is_cancelled (abstract))
+		return DC_STATUS_CANCELLED;
+
 	// Flush the serial input buffer.
 	int rc = serial_flush (device->port, SERIAL_QUEUE_INPUT);
 	if (rc == -1) {

src/hw_frog.c

@@ -111,6 +111,9 @@ hw_frog_transfer (hw_frog_device_t *device,
 {
 	dc_device_t *abstract = (dc_device_t *) device;
 
+	if (device_is_cancelled (abstract))
+		return DC_STATUS_CANCELLED;
+
 	// Send the command.
 	unsigned char command[1] = {cmd};
 	int n = serial_write (device->port, command, sizeof (command));

src/hw_ostc3.c

@@ -108,6 +108,9 @@ hw_ostc3_transfer (hw_ostc3_device_t *device,
 {
 	dc_device_t *abstract = (dc_device_t *) device;
 
+	if (device_is_cancelled (abstract))
+		return DC_STATUS_CANCELLED;
+
 	// Send the command.
 	unsigned char command[1] = {cmd};
 	int n = serial_write (device->port, command, sizeof (command));

src/mares_iconhd.c

@@ -122,6 +122,9 @@ mares_iconhd_transfer (mares_iconhd_device_t *device,
 
 	assert (csize >= 2);
 
+	if (device_is_cancelled (abstract))
+		return DC_STATUS_CANCELLED;
+
 	// Send the command header to the dive computer.
 	int n = serial_write (device->port, command, 2);
 	if (n != 2) {

src/shearwater_common.c

@@ -266,6 +266,9 @@ shearwater_common_transfer (shearwater_common_device_t *device, const unsigned c
 	if (isize > SZ_PACKET || osize > SZ_PACKET)
 		return DC_STATUS_INVALIDARGS;
 
+	if (device_is_cancelled (abstract))
+		return DC_STATUS_CANCELLED;
+
 	// Setup the request packet.
 	packet[0] = 0xFF;
 	packet[1] = 0x01;

src/zeagle_n2ition3.c

@@ -79,6 +79,9 @@ zeagle_n2ition3_packet (zeagle_n2ition3_device_t *device, const unsigned char co
 
 	assert (asize >= csize + 5);
 
+	if (device_is_cancelled (abstract))
+		return DC_STATUS_CANCELLED;
+
 	// Send the command to the device.
 	int n = serial_write (device->port, command, csize);
 	if (n != csize) {