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Modified si470x driver that works with Sparkfun FM Tuner Basic Breakout
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A20_si470x_reset A20 support to initialize si470x in i2c mode May 18, 2016
Kconfig original driver May 18, 2016
Makefile original driver May 18, 2016 Update May 18, 2016
radio-si470x-i2c.c modified si470x driver without interruptions May 18, 2016

Modified SI470X V4L2 driver


This project is about interfacing SI470X with A20 SoC (Olinuxino LIME). The unused TWI2 was selected because the tuner chip has a non-standard i2c initialization and needs SDA pin usage exclusivity.


 |-----------|                                  |---------------|
 |           |- LOUT ------------------- FMINL -|               |
 | breakout  |- ROUT ------------------- FMINR -|   Olinuxino   |
 |           |- VCC --------------------- 3.3v -|     A20       |
 |           |- GND ---------------------- GND -|               |
 |           |- SDIO -------------------- PB21 -|               |
 |           |- SCLK -------------------- PB22 -|               |
 |           |- SEN xD                          |               |
 |           |- RST --------------------- PC18 -|               |
 |-----------|                                  |---------------|

Also, I removed R8 and R3 resistors from Sparkfun breakout [4] because Olinuxino board already has built-in open drain pull up resistors [1].


The untouched kernel driver does not work because:

  • There is no defined IRQ for the device
  • The initialization routine leave the chip in an undefined state.

To fix this, what I did was cold start:

  • Power down the chip with ENABLE|DISABLE flags (according to page 5 [3])
  • Set external crystal
  • Wait 500 ms for calibration
  • Enable the chip again

And also, I deleted any interruptions related code 0:) (sadly RDS support is not working).

Once you install the modified driver, you can load it as follows:

	modprobe radio_i2c_si470x
	echo "si470x 0x10" > /sys/bus/i2c/devices/i2c-2/new_device

reset_tuner_si470x is a program included in this repository. If you want to know how the last line works, please check

0x10 is the i2c device address. You can get it with i2cdetect -y 2 command.

Later, you can tune any FM radio frequency via /dev/radio0 V4L2 interface. The project is useful for you here.

Audio capturing

sunxi codec

Diagram above [2] says first value ADCIS=1 corresponds to FMin. ALSA sunxi codec driver has a control "ADC Input Mux" to select the audio source for capturing, configured as a 7 state percentage bar. If 100/7=˜14, the first value in the bar (14) is for FMin. sunxi codec

Finally!, you can test the radio output:

Terminal 1

arecord -D hw:0,0 -c 2 -V stereo /dev/null

Terminal 2

fm -d /dev/radio0 -t 0 -T forever 89.70 100%


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