Using a system call to ‘amidi’ seemed a bit slow. While searching the Net I found that ‘mido’ also supports ‘amidi’ as a backend but the documentation clearly states that it is very heavy to make system calls each time.
So I kept searching. Maybe opening ‘amidi’ just once and redirecting commands through a pipe? No, it doesn’t like allow.
But… found aMIDIcat:
It hooks up standard input, and standard output, to the ALSA sequencer.
This makes it easy to pipe data around.
Yes, yes! Ubuntu says ‘amidicat’ is included in ‘sndio-tools’ but after installing this package in ev3dev the command was not found so I download the source code and compiled it (very short, very fast, just use ‘make’).
And it works!
echo "903C7F" | ./amidicat --port 128:0 --hex
Even better: it works directly to ‘multimidicast’ so no need to load the ‘snd-virmidi’ kernel module and connect it to ‘multimidicast’.
So I create a pipe:
mkfifo midipipe
and in my python/micropython script I just open the pipe and write to it:
pipe = open("./midipipe", "w")
pipe.write("903C7F")
so no need to use ‘os.system’ at all!
The gain was huge: I can now send several notes in a row and they sound like they were played at the same time (a chord); with system calls to ‘amidi’ the delay between each system call was clearly noticeable.
I still have the problem that sooner or later a note stucks and I need to send a ‘all notes off’ (“B0 7B 00”) MIDI command. But for now I can live with it (of course, my wife -the musician that will use the LEGO ipMIDI instrument – will not).