TS-7970 3.5mm Audio Ports
The TS-7970 includes two 3.5mm jacks. The top port is a mono microphone input, and the bottom port is a headphone port with left and right channels. Use "alsamixer" or "amixer" to adjust the volume.
In Linux select between the HDMI and 3.5mm ports with an alsa variable. By default all audio comes out of the sgtl5000 for the 3.5mm ports.
# list the sound cards aplay -l export ALSA_CARD=imxhdmisoc espeak "this is playing from the HDMI monitor" ## On kernel 4.1: #export ALSA_CARD=imx6qts7970sgtl ## On kernel 4.9 export ALSA_CARD=Codec espeak "this is playing from the onboard sgtl5000"