Control; Host Control - XMOS xCORE-200 Multi-channel Audio board Design Manual

USB Audio Design Guide
The inputs from the audio interface on the device—these samples come from
the audio driver.
Since the sum of these inputs may be more then the 18 possible mix inputs to
each mixer, there is a mapping from all the possible inputs to the mixer inputs.
After the mix occurs, the final outputs are created. There are two output destina-
tions:
The USB inputs to the host—these samples are sent to the decoupler core.
The outputs to the audio interface on the device—these samples are sent to the
audio driver.
For each possible output, a mapping exists to tell the mixer what its source is.
The possible sources are the USB outputs from the host, the inputs for the audio
interface or the outputs from the mixer units.
As mentioned in §3.3.3.3, the mixer can also handle volume setting. If the mixer
is configured to handle volume but the number of mixes is set to zero (so the
component is solely doing volume setting) then the component will use only one
core.

3.6.1 Control

The mixers can receive the following control commands from the Endpoint 0 core
via a channel:
Command
SET_SAMPLES_TO_HOST_MAP
SET_SAMPLES_TO_DEVICE_MAP
SET_MIX_MULT
SET_MIX_MAP
SET_MIX_IN_VOL
Figure 16:
Mixer
SET_MIX_OUT_VOL
Component
Commands

3.6.2 Host Control

The mixer can be controlled from a host PC by sending requests to Endpoint 0.
XMOS provides a simple command line based sample application demonstrating
how the mixer can be controlled.
For details, consult the README file in the host_usb_mixer_control directory.
XM0088546.1
Description
Sets the source of one of the audio streams going to the
host.
Sets the source of one of the audio streams going to the
audio driver.
Sets the multiplier for one of the inputs to a mixer.
Sets the source of one of the inputs to a mixer.
If volume adjustment is being done in the mixer, this
command sets the volume multiplier of one of the USB
audio inputs.
If volume adjustment is being done in the mixer, this
command sets the volume multiplier of one of the USB
audio outputs.
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