Problem in adding custom DAC in Volumio

Darmur · June 29, 2020, 2:40pm

During the weekend I managed to compile the driver for the TFA9879 (part of the bassfly-uhat).

Selecting the dt-overlay I can see the DAC in alsa and I can play sound with speaker-test

I followed those instructions to add compatibility to Volumio

I can select the added DAC in the playback options, the config.txt file is modified correctly after the selection

Volume control with HW Mixer woks fine (I can see the updated value from alsamixer if I change volume from Volumio)

Unfortunately I can’t hear any audio coming out from the speaker if I start the playback, I also don’t get any error

What can I do for checking what’s happening? It looks like the output is not selected correctly

balbuze · June 29, 2020, 2:57pm

Have you tried to resample?

Darmur · June 29, 2020, 3:09pm

Not yet, I will. Thanks for the hint

Darmur · June 29, 2020, 3:17pm

You were right, activating the resampler made it working

Next step is to make it stereo, I need to learn how to modify the .dts

volumio · June 30, 2020, 9:26am

Hi!
I would suggest at this point that in the alsa driver you state that only 24 bits is supported in this DAC, this way it would not need resampling enabled (alsa will take care of it)

Darmur · June 30, 2020, 10:08am

Yes, the IC is capable of handling 24bits, I need to have a look to the driver source code and patch it for handling 24bits

volumio · June 30, 2020, 10:37am

If you point me at the sources of the driver that you’re starting with I can give you an hint

Darmur · June 30, 2020, 3:45pm

Sure, here the driver I’m using

github.com

raspberrypi/linux/blob/rpi-4.19.y/sound/soc/codecs/tfa9879.c

// SPDX-License-Identifier: GPL-2.0+
//
// tfa9879.c  --  driver for NXP Semiconductors TFA9879
//
// Copyright (C) 2014 Axentia Technologies AB
// Author: Peter Rosin <peda@axentia.se>

#include <linux/module.h>
#include <linux/init.h>
#include <linux/i2c.h>
#include <linux/regmap.h>
#include <sound/soc.h>
#include <sound/tlv.h>
#include <sound/pcm_params.h>

#include "tfa9879.h"

struct tfa9879_priv {
	struct regmap *regmap;
	int lsb_justified;

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github.com

raspberrypi/linux/blob/rpi-4.19.y/sound/soc/codecs/tfa9879.h

/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * tfa9879.h  --  driver for NXP Semiconductors TFA9879
 *
 * Copyright (C) 2014 Axentia Technologies AB
 * Author: Peter Rosin <peda@axentia.se>
 */

#ifndef _TFA9879_H
#define _TFA9879_H

#define TFA9879_DEVICE_CONTROL		0x00
#define TFA9879_SERIAL_INTERFACE_1	0x01
#define TFA9879_PCM_IOM2_FORMAT_1	0x02
#define TFA9879_SERIAL_INTERFACE_2	0x03
#define TFA9879_PCM_IOM2_FORMAT_2	0x04
#define TFA9879_EQUALIZER_A1		0x05
#define TFA9879_EQUALIZER_A2		0x06
#define TFA9879_EQUALIZER_B1		0x07
#define TFA9879_EQUALIZER_B2		0x08

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This is the datasheet, of the amplifier, it supports I2S format with up to 24bit data

noiro · June 30, 2020, 5:34pm

I see progress Dario! Well done!

Darmur · June 30, 2020, 6:31pm

Yes, very happy about the progress!

I’m becoming more and more familiar with the process, soon I’ll try to build driver for TAS5825M too!

noiro · June 30, 2020, 7:47pm

I am waiting for that