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Radio Si740x on Olinuxino A20

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

Project

Pinout

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

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

Software

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:

	reset_tuner_si470x
	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 https://www.kernel.org/doc/Documentation/i2c/instantiating-devices.

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 http://benpfaff.org/fmtools/ 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%

Source code

https://github.com/astroza/si470x

References