What driver to use for that "custom" DAC

[hansipete]

Hi there,

I’m working on a Raspberry Pi (B+) project that should output audio through an FM transmitter IC. Right now I’m using the analog input, but I’d like to switch over to I2S, as the transmitter IC features a “digital mode”.

The mentioned IC is a 4713 by Silicon Labs. Their datasheet gives a minimal example how to use the digital mode:

I left out the resistors and connected DCLK, DIN, DFS directly to the Raspberry PCM_CLK, PCM_DOUT, PCM_FS.

It’s unclear to me, how to output the I2S to the transmitter IC? Which driver to use? I’m running latest and up to date Rasbian image on the Pi. I tried to load drivers for the HifiBerry, etc. and thought the might work with my IC, too. — no result.

The datasheet (silabs.com/Support%20Documen … 13-B30.pdf, P.23) says not much about the digital mode — mainly:

The digital audio interface operates in slave mode and supports 3 different audio data formats:

1. I2S
2. Left-Justified
3. DSP Mode
   5.4.1. Audio Data Formats
   In I2S mode, the MSB is captured on the second rising edge of DCLK following each DFS transition. The remaining bits of the word are sent in order, down to the LSB. The Left Channel is transferred first when the DFS is low, and the Right Channel is transferred when the DFS is high.

— and:

The device supports DCLK frequencies above 1 MHz.

Can someone push me in the right direction, what software/drivers I need to install/use? The described I2S mode in the datasheet — is it “standard” and compatible with the Raspberry, or some proprietary thingi?

Thanks in advance & Regards,
Hans

[IRoN]

Hello,

Hifiberry and generic should work without any changes

But for now I2S output doesnt work correctly on B+ … (some changes have to be made in the kernel)

Take a look at tjaekel website about that

[hansipete]

Thank you so much — This information helps a lot! So i don’t have to try further for now…

I think the model naming of the Raspberries is a bit problematic. There was the B in two revisions, and now there is the B+. This makes searching forums and the internet hard. I could not find clear information about I2S on the B+ in all places I looked for it.

Again — thank you! I’ll have a look at tjaekels site

[hansipete]

Hi there — good news: my transmitter was playing I2s today!

Here is what I did:

• Flashed SD card with newest raspbian image, 2014-09-09
• To be save: rpi-update
• Tweaked modules and rpi-blacklist files, created asound.conf

This is what my /etc/modules looks like

[code]#enable i2c
i2c-bcm2708
i2c-dev

disable analog audio

#snd-bcm2835

#enable dac+ hifiberry i2s output
snd_soc_core
snd_soc_bcm2708_i2s
bcm2708_dmaengine
snd_soc_pcm1794a
snd_soc_rpi_dac[/code]

This is my /etc/modprobe.d/raspi-blacklist.conf

blacklist spi-bcm2708 #blacklist i2c-bcm2708 #blacklist snd-soc-pcm512x #blacklist snd-soc-wm8804

Now I can play using aplay or mplayer. I just need to find out how to keep the PCM_DCLK and PCM_FS clocks up, when I don’t play any sound. My radio transmitter IC will leave I2S mode, when the clock signals are dead.

Thanks for your help!