I've been implementing custom devices for stage music use for several years, using small SBCs that run a basic RTOS that I code up myself. The input and output is MIDI, coded music tokens (not digitised audio) at a serial data rate of 31.25 KB. Even with the maximum amount of processing involved, latency time between receipt of a byte and its associated transmission was never more than a millisecond or so.
The main limitation has been HMI, for that reason I'm looking at moving to a SBC that can support USB so that I can connect to a tablet or palm device. What I'm finding is that boards that support the sort of interfaces that will talk to eg. a tablet, are often really slow in comparison. Based on information I've managed to glean, many of these systems are likely to introduce throughput delays of 30mS or longer, even for a 2-line program loop read char/send char.That's getting to be too long for music.
The OS involved, usually Linux, is one contributor, random processing holdups of > 10mS for system housekeeping are cited. One system I checked out doesn't use interrupts for the serial ports that MIDI uses, it just polls them at about 100 Hz, adding another potentially 20mS to the round trip.
What I'm after is a small SBC that has reasonable support for USB comms, and also can guarantee turnround of only a few mS for low level I/O such as serial comms. Does anyone have any suggestions? TIA