Blackboard audio I/O through ALSA?

Jonathan · 16 June 2020 21:10

is it possible for a program to access the audio input and output on the Blackboard through ALSA?

Gustav · 18 June 2020 08:12

Hi Jonathan and welcome to the forums. To answer the question, no, you cannot access the audio ports through ALSA. Mainly due to the lack of drivers. Elk and Elkpi was built for realtime applications and as such has a different hw design compared to say a USB soundcard.

Stefano · 18 June 2020 15:09

Hi @Jonathan,
on top of Gustav’s answer, there is indeed an ALSA driver for the codec that we use in the mainline Kernel:

github.com

torvalds/linux/blob/master/sound/soc/codecs/pcm3168a.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * PCM3168A codec driver
 *
 * Copyright (C) 2015 Imagination Technologies Ltd.
 *
 * Author: Damien Horsley <Damien.Horsley@imgtec.com>
 */

#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/module.h>
#include <linux/of_gpio.h>
#include <linux/pm_runtime.h>
#include <linux/regulator/consumer.h>

#include <sound/pcm_params.h>
#include <sound/soc.h>
#include <sound/tlv.h>

This file has been truncated. show original

but it doesn’t take into accout the tricks that we are doing with the CPLD on the Elk PI to tweak the bitclock in order to support 8 channels on the RPi.

If you have enough knowledge with Linux drivers, you could take a look at modifying that using as a reference our RTDM driver for the same codec:

Jonathan · 18 June 2020 20:58

Thanks for the quick replies and the source code link, I really appreciate it.
I didn’t really need ALAS I/O for anything (I don’t know C or driver programming anyways), it was mostly out of curiosity.