How to make use of -Mm flag for multiple input ports?

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This feature to enable access to multiple midi ports was added in 6.14, but I can’t figure out how to make use of it in ctrl7 (for example).

Say I want to use channel 3 of port 2, that would be channel 18 according to the docs, but I get an error when I plug that number into the ctrl7 opcode (which accepts 1-16). Any ideas what I’m missing?

thanks

i have made a feature request feature request: several midi ports #1750
that looks somewhat like yours. I am looking for inputs and outputs for more than 1 midi port.
As i understand, channels >16 for inputs are possible when you use the PortMidi driver.

So far i have been unsuccessful at isolating a certain keyboard on different midi input ports.
Were you able to do so?