3.2
Audio
3.2.1
Description
The audio microcontroller on M400C bridges the internal DSP to the USB interface. The micro-
controller enumerates as a USB sound card (UAC 1.0) and a virtual COM port (CDC). The micro-
controller can receive commands via the COM port to change audio use cases or USB modes.
Serial communication with the virtual COM port uses 9600 baud 8N1 format.
3.2.2
Audio Modes
The audio use case can be changed using the virtual COM port endpoint. The microcontroller will
use the Direct Playback and Direct Record modes by default after powering up. Commands need
to terminated with the end of line character “
\r
”.
The “
splay
” command changes the playback use case and the “
srec
” command changes
the record use case. The syntax of both commands is:
splay USE_CASE_NAME
srec USE_CASE_NAME
Table 3.4 shows the valid values of “
USE_CASE_NAME
” for each supported mode.
Use Case
USB API Name
Direct Playback
direct_playback
Direct Record
direct_record
Live Record
live_record
Personal Record
personal_record
Table 3.4: Use Case Names for Audio API
If the command is successful, the microcontroller will respond with an “
ok
” message and
restarts in the selected mode. If there is an issue the microcontroller will respond with “
Error
”.
The current playback or record mode can be queried with the “
gplay
” and “
grec
” commands.
3.2.3
Summary of Commands
Below is a list of valid commands to the audio microcontroller virtual COM port:
splay direct_playback
srec personal_record
srec live_record
srec direct_record
gplay
grec
26
Revision 7
Vuzix Corporation
