[PATCH] RTL-SDR: Fix regression in FC00012 tuner startup (needs testing on FC2580)

David Basden shigawire at gmail.com
Sun Feb 4 12:50:23 UTC 2018

This patch fixes a regression of rtl-sdr dongles with the FC00012 tuner.

The code to switch on the FC00012 tuner by pulling it's ~RESET line
low ended up with an off-by-one error in a refactor a long time ago,

The FC00012 only continued to work by accident as a different bug in
rtlsdr_set_gpio_output had a side-effect of pulling low the FC00012's
~RESET line

When the rtl_set_gpio_output bug was fixed in ba64a7459a43 the side-
effect also went away, leaving the FC00012 tuner in reset, and failing
to be detected (or indeed work at all).

This patch fixes the original off-by-one error.  It's been tested
on an FC00012 in a GTek T803 from both warm and cold starts, but needs
testing on the FC2580 as both the FC00012 and FC2580 are brought out of
reset by a GPIO off the RTL (at least in some designs). If the FC2580
actually uses a different pin, this code will also break.  (I'm only going
from vague memory that the FC2580 used the same pin.)

 src/librtlsdr.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/librtlsdr.c b/src/librtlsdr.c
index b369a5d..678fadd 100644
--- a/src/librtlsdr.c
+++ b/src/librtlsdr.c
@@ -1565,11 +1565,11 @@ int rtlsdr_open(rtlsdr_dev_t **out_dev, uint32_t

  /* initialise GPIOs */
- rtlsdr_set_gpio_output(dev, 5);
+ rtlsdr_set_gpio_output(dev, 4);

  /* reset tuner before probing */
- rtlsdr_set_gpio_bit(dev, 5, 1);
- rtlsdr_set_gpio_bit(dev, 5, 0);
+ rtlsdr_set_gpio_bit(dev, 4, 1);
+ rtlsdr_set_gpio_bit(dev, 4, 0);

  reg = rtlsdr_i2c_read_reg(dev, FC2580_I2C_ADDR, FC2580_CHECK_ADDR);
  if ((reg & 0x7f) == FC2580_CHECK_VAL) {
@@ -1581,7 +1581,7 @@ int rtlsdr_open(rtlsdr_dev_t **out_dev, uint32_t
  reg = rtlsdr_i2c_read_reg(dev, FC0012_I2C_ADDR, FC0012_CHECK_ADDR);
  if (reg == FC0012_CHECK_VAL) {
  fprintf(stderr, "Found Fitipower FC0012 tuner\n");
- rtlsdr_set_gpio_output(dev, 6);
+ rtlsdr_set_gpio_output(dev, 5);
  dev->tuner_type = RTLSDR_TUNER_FC0012;
  goto found;
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