* Added USB audio rendering using USB Audio Class 2 Ref: remake-v0.3
Currently, only 192000kHz & 32bit audio format was supported.
The audio codec supports multiple layers of volume/gain configurations for different elements. However, only the feature unit with volume control just before the end of output terminal will be used as the overall volume control. 64da0dc2fa2a438d14f6d29fb2357af368ce0a3b
Probably only the DAC volume should be reported, or try to linearize the analog attenuations. Other units may be controlled using the HID vendor report and dedicated host application.
High-speed asynchronous isochronous endpoint (8kHz) with feedback endpoint (1kHz) was used for audio output, to ensure no buffer overrun/underrun and reduce latency.
Dedicated endpoint 1 interrupts was used for audio endpoints, to reduce latency in calling audio processing functions. STM32 seems forcing NAKs to isochronous endpoints if enabled too late / at inappropriate times, results in audio randomly stopped working.
To enable dedicated endpoint interrupts, registers DEACHINT, DEACHMSK and DOUTEP1MSK/DINEP1MSK need to be used. While DEACHINT and DEACHMSK were documented in the STM32F72 reference manual (rev 1), DOUTEP1MSK and DINEP1MSK were not. They are documented in the STM32F42 reference manual (rev 13) and are defined in the header files. Ref: 98f132bba9c94cd500419340bd4b8075443fc399
The mysterious interrupt flag causing endpoint 0 to stop firing interrupts after received data packets was also found. There are apparently an OTEPSPR bit in the DOEPINT register and an OTEPSPRM bit in the DOEPMSK register, defined in the header files as “Status Phase Received For Control Write” and “Status Phase Received mask”. However, they were not mentioned anywhere in STM32F72 and STM32F42 reference manuals. Ref: f1094f83f84872099f925fe712ae05f483ff4699
The sideway RGB LEDs have built-in reverse zener(?) diodes to protect green and blue LEDs (why not red?). This requires open-drain cathode controls. Otherwise, current can still flow through the diodes: 
Ref: MSL0104RGB Series Ref: 66c5f3891aad4c7d8f02718bb6facaa1c5a482bd