Linux Audio Support¶
Audio support for linux is based on the Linux for Qualcomm Software support.
Development Board Configuration¶
Power¶
Ensure that Switch S7 is set properly to power the SGTL5000 Codec chip:- Switch 3 should be set to enable Audio, which is a top level enable to send 1.8 V to the audio codec chip SGTL5000XNBA3 (U16).
- Switch 4 can be either set or not set
- If Switch 4 is not set the 1.8V comes from the DC supply on the Development Kit
- If Switch 4 is set the 1.8V comes from the SOM
Audio Interface Options¶
There are two available interfaces for audio input/output:
- The J8 AUDIO 3.5 mm jack that supports stereo headset with mono microphone:
- The J23 LINEIN/LINEOUT Header
Headset Examples¶
This section details how to validate AUDIO jack J8.
Configuration¶
The following steps will configure the SGTL5000 Codec chip to utilize the Headset for input and output.
# Set Playback volume high so it can be heard tinymix set 'PCM Playback Volume' 160 160 # Set capture volume high so we can hear what we capture tinymix set 'Capture Volume' 15 15 # Capture is quiet enough, don't further attentuate tinymix set 'Capture Attenuate Switch (-6dB)' 0 # Enable Zero Crossing capture switch to minimize popping tinymix set 'Capture ZC Switch' 1 # Enable Capture switch so we can record audio input tinymix set 'Capture Switch' 1 # Set Headphone playback volume to halfway so its loud enough to be heard clearly tinymix set 'Headphone Playback Volume' 63 63 # Enable headphone playback tinymix set 'Headphone Playback Switch' 1 # Enable headphone zero crossing switch to limit popping tinymix set 'Headphone Playback ZC Switch' 1 # Increase mic volume since recordings are always so quiet tinymix set 'Mic Volume' 2 # Select MIC_IN for capture tinymix set 'Capture Mux' 0 # Select DAC as output for Headphones tinymix set 'Headphone Mux' 0 # Select I2S for what feeds into DAC for output (skip DAP) tinymix set 'Digital Input Mux' 1
Headphones Audio Out¶
Below are a number of examples of how to play audio:- Play 400 Hz tone in stereo
gst-launch-1.0 audiotestsrc ! audioconvert ! audio/x-raw,channels=2 ! alsasink
- Play 400 Hz tone left channel only
gst-launch-1.0 audiotestsrc ! audiochannelmix left-to-left=1 right-to-left=1 right-to-right=0 ! alsasink
- Play 400 Hz tone right channel only
gst-launch-1.0 audiotestsrc ! audiochannelmix left-to-left=0 left-to-right=1 right-to-right=1 ! alsasink
- Play .wav file (see attachement) with vumeter
paplay LRMonoPhase4.wav -v
Recording Headset Mic Audio¶
Below is an example of recording audio with an active vumeter to indicate intensity of audio being recorded:
arecord -f dat --vumeter=mono test_mic.wav
LINEIN/LINEOUT Examples¶
This section details how to validate LINEIN/LINEOUT header J23.
Configuration¶
The following steps will configure the SGTL5000 Codec chip to utilize LINEIN and LINEOUT.
# Set Playback volume high so it can be heard tinymix set 'PCM Playback Volume' 160 160 # Set capture volume high so we can hear what we capture tinymix set 'Capture Volume' 15 15 # Capture is quiet enough, don't further attentuate tinymix set 'Capture Attenuate Switch (-6dB)' 0 # Enable Zero Crossing capture switch to minimize popping tinymix set 'Capture ZC Switch' 1 # Enable Capture switch so we can record audio input tinymix set 'Capture Switch' 1 # Set line out playback to halfway so it's loud enough to be heard clearly tinymix set 'Lineout Playback Volume' 15 15 # Enable Line out tinymix set 'Lineout Playback Switch' 1 # Select LINE_IN for capture tinymix set 'Capture Mux' 1 # Select I2S for what feeds into DAC for output (skip DAP) tinymix set 'Digital Input Mux' 1
LINEOUT Audio Out¶
Follow steps in Headphones Audio Out
Recording LINEIN Audio¶
Follow steps in Recording Headset Mic Audio
Additional Details¶
The following sections provide additional details regarding audio in the MitySOM-QC Development Kit.
Hardware Overview¶
A hardware block diagram of the audio subsystem is shown below. The following components are involved on the MitySOM-QC6490 devkit:
- Application processor – This is the ARM CPU complex and handles audio processing tasks, including:
- Managing audio record and playback
- Decoding audio formats
- Using LPAI for postprocessing tasks
- Low Power AI (LPAI) – Subsystem that runs audio playback/record and voice-activation (VA) algorithms. It integrates with a dedicated Qualcomm® Hexagon™ Processor (QDSP6) and a low power island (LPI).
- Audio codec – For the devkit this is a SGTL5000 and it is connected to the LPAI via I2S0 connections. It provides:
- Analog-to-Digital Converter (ADC) for capturing microphone / line-in signals and converting them to I2S
- Digital-to-Analog Converter (DAC) for converting stereo I2S data to analog outptus for either the Headphones or line-out signals
- Headphone / Mic Jack
Additional information can be found on Qualcomm's Audio Overview page
SGTL5000 CODEC and Controls¶
The linux SGTL5000 codec driver includes several controls for the routing and data within the SGTL5000 chip (between the jacks and the I2S0 bus). A top level block diagram of the SGTL5000 is shown below:
From the picture, the 3 signal audio jack is connected to the Headphone outputs (stereo) and microphone inputs (mono) for use with a standard analog headset with microphone. The line in and line out signals are routed to the expansion header J23. By default, playback commands will be routed to the HeadPhone interface and capture commands will capture from the microphone input.
The available controls of the output SGTL5000 codec can be listed (along with their settings) with the tinymix command as shown below.
root@qcs6490-mitysom-devkit:~# tinymix contents Number of controls: 28 ctl type num name device value 0 INT 2 PCM Playback Volume 0144, 144 (range 0->192) 1 INT 2 Capture Volume 012, 12 (range 0->15) 2 BOOL 1 Capture Attenuate Switch (-6dB) 0Off 3 BOOL 1 Capture ZC Switch 0On 4 BOOL 1 Capture Switch 0On 5 INT 2 Headphone Playback Volume 0110, 110 (range 0->127) 6 BOOL 1 Headphone Playback Switch 0On 7 BOOL 1 Headphone Playback ZC Switch 0On 8 INT 1 Mic Volume 00 (range 0->3) 9 INT 2 Lineout Playback Volume 016, 16 (range 0->31) 10 BOOL 1 Lineout Playback Switch 0Off 11 INT 1 DAP Main channel 032768 (range 0->65535) 12 INT 1 DAP Mix channel 00 (range 0->65535) 13 BOOL 1 AVC Switch 0Off 14 BOOL 1 AVC Hard Limiter Switch 0Off 15 INT 1 AVC Max Gain Volume 01 (range 0->2) 16 INT 1 AVC Integrator Response 01 (range 0->3) 17 INT 1 AVC Threshold Volume 012 (range 0->96) 18 INT 1 BASS 0 047 (range 0->95) 19 INT 1 BASS 1 047 (range 0->95) 20 INT 1 BASS 2 047 (range 0->95) 21 INT 1 BASS 3 047 (range 0->95) 22 INT 1 BASS 4 047 (range 0->95) 23 ENUM 1 Capture Mux 0> MIC_IN, LINE_IN, 24 ENUM 1 Headphone Mux 0> DAC, LINE_IN, 25 ENUM 1 Digital Input Mux 0ADC, > I2S, Rsvrd, DAP, 26 ENUM 1 DAP Mux 0> ADC, I2S, 27 ENUM 1 DAP MIX Mux 0> ADC, I2S,
Note: the tinymix command does not put a space between the device number (always "0" in this case) and the settings.
In this case, the 'PCM Playback Volume' represents the digital DAC Volume Control, the 'Headphone Playback Volume' represents the analog gain on the Headphone volume control, the 'Capture Volume' represents the Analog Gain block entering the ADC, and the 'Mic Volume' represents the MIC GAIN block.
The tinymix tool can be used to adjust these settings. For example, to increase the analog output volume of the headphones channel:
tinymix set 'Headphone Playback Volume' 120 120
This will set both the left and right channel gain setting to be "120".
Below is the same top level diagram (shown above) for the SGTL5000 codec with some of the tinymux control names added for clarity:
There are other features of the codec not discussed here (including routing the audio through the Digital Audio Processor(DAP)) that can be leveraged in a similar manner.
See the SGTL5000 Datasheet for further details.
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