apply steve-m/librtlsdr/pull/58

src/librtlsdr.c

@@ -537,6 +537,7 @@ uint16_t rtlsdr_demod_read_reg(rtlsdr_dev_t *dev, uint8_t page, uint16_t addr, u
 int rtlsdr_demod_write_reg(rtlsdr_dev_t *dev, uint8_t page, uint16_t addr, uint16_t val, uint8_t len)
 {
 	int r;
+		int retries = 2;
 	unsigned char data[2];
 	uint16_t index = 0x10 | page;
 	addr = (addr << 8) | 0x20;
@@ -548,13 +549,18 @@ int rtlsdr_demod_write_reg(rtlsdr_dev_t *dev, uint8_t page, uint16_t addr, uint1
 
 	data[1] = val & 0xff;
 
+
 	r = libusb_control_transfer(dev->devh, CTRL_OUT, 0, addr, index, data, len, CTRL_TIMEOUT);
 
+	do {
+		r = libusb_control_transfer(dev->devh, CTRL_OUT, 0, addr, index, data, len, CTRL_TIMEOUT);
+		rtlsdr_demod_read_reg(dev, 0x0a, 0x01, 1);
+		retries--;
+	} while (retries > 0 && r < 0);
+
 	if (r < 0)
 		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);
 
-	rtlsdr_demod_read_reg(dev, 0x0a, 0x01, 1);
-
 	return (r == len) ? 0 : -1;
 }