This week, I continued to explore options for communication between the driving PC, the WaveShaper, and additional MIDI peripherals. Earlier this week, I had considered and sketched out a protocol wherein all auxiliary (i.e., non-MIDI) information would be transferred within the SysEx commands of the MIDI spec. While this is still feasible and should be able to keep up for live, real-time music, the USB specification enables the use of “composite devices” which support multiple, simultaneous interfaces. This could lend itself to more flexibility and warrants more analysis before setting in the serial communication in stone. From an ease of implementation point of view, it would have the advantage of having convenient parallelism between these conceptually disjoint streams without the need for additional hardware or cables.
(This design decision was prompted with the choice for the DEC-10 FPGA in mind, seeing as it supports both USB host and device interfaces.)
We would want to consider support the following serial streams.
- PC to the WaveShaper for MIDI notes and events.
- PC to the WaveShaper for a “shell”-like command interface.
- WaveShaper to PC for probing into the sound synthesis datapath.
- WaveShaper to PC for responses to “shell” commands.
- [Optional] A final USB audio input interface which can enable the PC to be used as a speaker / audio sink.
These could all be interfaced through dedicated, corresponding USB device classes.
While it would be incredibly helpful to offload the multiplexing to the USB hardware and controllers, I would want to revise the hardware we are deciding on more thoroughly before making such a jump. That said, the option remains to merely implement the first MIDI with SysEx interface (which would be in line with the original plan).