SerialMidi driver module
------------------------
v0.01 1/7/23

This module is a serial port driver for the Midi Support system
and should be placed in the MidiSupport Drivers directory.

It will search for up to 2 available serial UART ports. If any are
found they will be registered with midi support by their device
names i.e "Serial1" "Serial2" etc. Ports will be used even if there
is no midi hardware attached (the opto isolator bits) because the
software has no way of detecting this.

If you want to use a UART for something else, unload the
SerialMIDI module, connect your serial software to the UART, then
reload the SerialMIDI module.

Currently, the HAL in my PI only provides 1 UART (Serial1) and the
enclosed circuit diagram shows the pin numbers on the expansion
header for this UART.

Regarding the hardware adapter, to do a loop back test it is
ok to link the UART Tx and Rx pins together with no additional
hardware but to connect to an external midi device the opto
isolator is needed. It provides electrical isolation between the
two pieces of MIDI kit which is a requirement of the spec.
The link is also a 5mA current loop which means that you cannot
guarantee the voltage levels on either of the receive pins
relative to the receiver ground.
