Teensy specific Serial data format

[jacobanana]

It is possible to specify inverted pins on UART ports when using Teensy. This is documented here: https://www.pjrc.com/teensy/td_uart.html under the Serial1.begin(baud, format) section.

For MIDI, the relevant formats are :

Format Name	Data Bits	Parity	RX Polarity	TX Polarity
SERIAL_8N1	8	None	Normal	Normal
SERIAL_8N1_RXINV	8	None	Inverted	Normal
SERIAL_8N1_TXINV	8	None	Normal	Inverted
SERIAL_8N1_RXINV_TXINV	8	None	Inverted	Inverted

This allows more flexibility with input and output circuits that may be inverting.

In order to configure the polarity, it is important to inherit the custom settings struct from DefaultSerialSettings instead of DefaultSettings

struct TXInvMidiSettings : public midi::DefaultSerialSettings
{
    static const uint16_t SerialFormat = SERIAL_8N1_TXINV; // Invert TX
};

MIDI_CREATE_CUSTOM_INSTANCE(HardwareSerial, Serial1, midi1, TXInvMidiSettings);

[franky47]

There might be special cases to handle for SofttwareSerial, which does not have this extra configuration input (see failing tests).