Using I2SC (Inter-IC Sound Controller)


Introduction

This page explains how to enable and configure I2SC from SAMA5D2 SoCs to an external codec, using MikroElektronika audio codec PROTO board as an example.

The Inter-IC Sound Controller (I2SC) provides a 5-wire, bidirectional, synchronous, digital audio link to external audio devices: I2SC_DI(ADCDAT), I2SC_DO(DACDAT), I2SC_WS(LRCLK), I2SC_CK(BCLK), and I2SC_MCK(MCLK) pins.

Characteristics:

  • Master, Slave, and Controller Modes
    • Slave: Data Received/Transmitted
    • Master: Data Received/Transmitted And Clocks Generated
    • Controller: Clocks Generated
  • Individual Enable and Disable of Receiver, Transmitter and Clocks
  • Configurable Clock Generator Common to Receiver and Transmitter
    • Suitable for a Wide Range of Sample Frequencies (f s ), Including 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, and 192 kHz
    • 32 f s to 1024 f s Master Clock Generated for External Oversampling Data Converters
  • Support for Multiple Data Formats
    • 32-, 24-, 20-, 18-, 16-, and 8-bit Mono or Stereo Format
    • 16- and 8-bit Compact Stereo Format, with Left and Right Samples Packed in the Same Word to Reduce Data Transfers
  • DMA Controller Interfaces the Receiver and Transmitter to Reduce Processor Overhead
    • One DMA Controller Channel for Both Audio Channels
  • Smart Holding Registers Management to Avoid Audio Channels Mix After Overrun or Underrun

MikroElektronika PROTO Audio Codec Board

The PROTO board can be used to test capture and playback on I2SC. More details regarding this board can be found on https://www.mikroe.com/audio-codec-proto-board

Prerequisites

  • Linux4sam 5.8 or newer or vanilla kernel 4.18 (driver only) or newer;
    • kernel must be compiled with SND_SOC_MIKROE_PROTO
  • available only on SAMA5D2 SoCs; can be tested with SAMA5D2 Xplained board:
    Controller I2S wire board connector
    i2s0 I2SC_MCK J17 - 23
    I2SC_CK J17 - 17
    I2SC_WS J17 - 22
    I2SC_DO J17 - 25
    I2SC_DI J17 - 26
    i2s1 I2SC_MCK J17 - 4
    I2SC_CK J17 - 5
    I2SC_WS J8 - 1
    I2SC_DO J9 - 3
    I2SC_DI J9 - 2

Wire setup

The I2SC pins must be connected to the codec in the following way:

I2SC PROTO codec
I2SC_CK SCK
I2SC_DI MISO
I2SC_DO MOSI
I2SC_WS ADCL (for capture)
I2SC_WS DACL (for playback)

Also, you will need to connect PROTO SDA (Data Input) and SCL (Clock Input) pins to a TWI interface.

Bellow you can see a picture with the I2SC0 and I2C0 connected to the PROTO board:

On Linux4sam 6.0 release, the i2s0_proto overlay can be used for the setup in the picture, with the following u-boot command:

=> bootm 0x24000000#kernel_dtb#i2s0_proto
## Loading kernel from FIT Image at 24000000 ...
   Using 'kernel_dtb' configuration
   Trying 'kernel@1' kernel subimage
     Description:  Linux4SAM Linux kernel
     Type:         Kernel Image
     Compression:  uncompressed
     Data Start:   0x240000e0
     Data Size:    3835928 Bytes = 3.7 MiB
     Architecture: ARM
     OS:           Linux
     Load Address: 0x22000000
     Entry Point:  0x22000000
     Hash algo:    crc32
     Hash value:   7fca0b0c
     Hash algo:    sha1
     Hash value:   45cbd1fe15c283ef26056917fb4e10e2ce6b30e4
   Verifying Hash Integrity ... crc32+ sha1+ OK
## Loading fdt from FIT Image at 24000000 ...
   Using 'kernel_dtb' configuration
   Trying 'base_fdt' fdt subimage
     Description:  Flattened Device Tree blob
     Type:         Flat Device Tree
     Compression:  uncompressed
     Data Start:   0x243a8a24
     Data Size:    44591 Bytes = 43.5 KiB
     Architecture: ARM
     Load Address: 0x23000000
     Hash algo:    crc32
     Hash value:   9c933a6d
     Hash algo:    sha1
     Hash value:   c249364df161f1158f084ab0191c034a519a9fdd
   Verifying Hash Integrity ... crc32+ sha1+ OK
   Loading fdt from 0x243a8a24 to 0x23000000
## Loading fdt from FIT Image at 24000000 ...
   Using 'i2s0_proto' configuration
   Trying 'fdt_i2s0_proto' fdt subimage
     Description:  Device Tree blob PROTO Audio board overlay
     Type:         Flat Device Tree
     Compression:  uncompressed
     Data Start:   0x243b9b64
     Data Size:    1066 Bytes = 1 KiB
     Architecture: ARM
     Load Address: 0x23170000
     Hash algo:    crc32
     Hash value:   38a511f6
     Hash algo:    sha1
     Hash value:   74d5c3996811a9307097969d8fe3c5e63b9973a0
   Verifying Hash Integrity ... crc32+ sha1+ OK
   Loading fdt from 0x243b9b64 to 0x23170000
   Booting using the fdt blob at 0x23000000
   Loading Kernel Image ... OK
   Loading Device Tree to 3fb47000, end 3fb54f5f ... OK

Starting kernel ...

Make sure the output of the bootm command is the same as above and that fdt_i2s0_proto overlay is applied .

Probing

If everything works well, at linux boot look for:

ALSA device list:
[...]
#2: wm8731 @ sama5d2_xplained

Another step to assure that we are using the right device is to search /proc file system:

# cat /proc/asound/pcm | grep -i wm8731
02-00: WM8731 HiFi wm8731-hifi-0 :  : playback 1 : capture 1

These steps are necessary to see if the drivers probed and to get the ALSA device id. In both prints, it is the first number on the line: 2 in our example. Also, we will need to find our complete device name:

# aplay -L
[...]
sysdefault:CARD=sama5d2xplain_1
wm8731 @ sama5d2_xplained, 
Default Audio Device

In this list, our board is the one with the wm8731 codec. In our case, the device’s name is: sysdefault:sama5d2xplain_1

Playback

First, we need to use amixer (or alsamixer) to enable the playback. We must enable 'Output Mixer HiFi Playback Switch' (replace –c 2 with your –c <ALSA device id>):

# amixer -c 2 cset name='Output Mixer HiFi Playback Switch' on
And we should see:
numid=13,iface=MIXER,name='Output Mixer HiFi Playback Switch'
; type=BOOLEAN,access=rw------,values=1
: values=on

Warning, importantWarning, importantWarning, important Before starting the playback, make sure that the I2SC_WS pin is connected to the DACL pin.

Insert headphones in the playback jack and check sound on both channels (replace -Dsysdefault:sama5d2xplain_1 with your device’s name):

# speaker-test -Dsysdefault:sama5d2xplain_1 -c 2

Capture

Use amixer (or alsamixer) to enable the playback (replace –c 2 with your –c <ALSA device id>):

# amixer -c 2 cset name='Input Mux' 1
numid=14,iface=MIXER,name='Input Mux'
; type=ENUMERATED,access=rw------,values=1,items=2
; Item #0 'Line In'
; Item #1 'Mic'
: values=1# amixer -c 2 cset name='Mic Capture Switch' on
numid=6,iface=MIXER,name='Mic Capture Switch'
; type=BOOLEAN,access=rw------,values=1
: values=on

Warning, importantWarning, importantWarning, important Before starting the record, make sure that the I2SC_WS pin is connected to the ADCL pin.

Connect a PC or a low impedance microphone to the Mic jack and start recording (replace –Dplughw:2 with your –Dplughw:<ALSA device id>):

# arecord -Dplughw:2 -c 2 -f S16_LE out.wav

Stop the recording after a few seconds and playback the resulting out.wav file. Make sure sound is on both channels (replace –Dplughw:2 with your –Dplughw:<ALSA device id>)

Warning, importantWarning, importantWarning, important Before starting the playback, make sure that the I2SC_WS pin is connected to the DACL pin

# aplay -Dplughw:2 out.wav
WebFaqBaseForm
Boards Sama5d2Xplained
Components Kernel, linux-4.9-at91, linux-4.14-at91
Summary How to use I2SC
r3 - 16 Nov 2018 - 16:26:26 - CodrinCiubotariu
 
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