Midi player on NUCLEO-F446RE

This project implements a midi player on a NUCLEO-F446RE board.

At the start of the program it reads the root directory of the sdcard of shows the list of files on the 128x64 OLED display. Turning the knob allows one to choose the file to be played. A push on the knob starts the playing.

The MIDI events are sent to the UART which is connected to the 5 pin DIN connector.

Software

The software is is built as an actor system. A class becomes an actor while inheriting from the Actor class.

These are the actors:

• Controller
• RotayButton

MIDI Parser

The parser is given an name of a MIDI file and starts readding the file. The extension of the file must be .mid. As the a NUCLEO-F446RE board has only 128kb of static RAM the parser avoids the buffering of the midi events in memory while reading the MIDI file. In order to make the parser more generally usefull it is given a lambda function which is used as a callback.

Not on every event this lambda function is called. The following table shows how each event is handled by the parser.

Meaning	Code	Action
Sequence number	FF 00	skip
Text	FF 01	skip
Copyright notice	FF 02	skip
Track name	FF 03	buffered, not used
Instrument name	FF 04	skip
Lyric text	FF 05	skip
Marker text	FF 06	skip
Cue point	FF 07	skip
Program name	FF 08	skip
Device name	FF 09	skip
MIDI channel prefix	FF 20	skip
MIDI port	FF 21	skip
Track end	FF 2F	stop
Tempo	FF 51	buffered, is used in the next delta to ms calculation
SMPTE offset	FF 54	skip
Time signature	FF 58	buffered, not used
Key signature	FF 59	buffered, not used
Key signature	FF 7F	skip
Note off	80	lambda called
Note on	90	lambda called
Polyphonic pressure	A0	skip
Controller	B0	lambda called
Program change	C0	skip
Channel pressure	D0	skip
Pitch bend	E0	skip
single SysEx	F0	skip
Escape sequence	F3	not detected
Escaped single SysEx	F7	skip

The Running status mechanism is handled correctly.

On parsing error a All Sound Off and All Notes Off message is sent.

Hardware

Connection sd card reader

In the source header file:

mbed-os/targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F446xE/TARGET_NUCLEO_F446RE/PinNames.h

the general names definitions for the for the SPI port can be found. For the F446RE these are the SPI definitions:

typedef enum {
    SPI_MOSI    = PA_7,
    SPI_MISO    = PA_6,
    SPI_SCK     = PA_5,
    SPI_CS      = PB_6,
} PinName;

Only the SPI definitions are mentioned in the preceding example.

OLED display

Source code from Adafruit is used to drive the display.

Rotary button decoder

The RotaryButton class is responsable for handling the reoary button. Due to contact bounce an interrupt solution was not possible. The RotaryButton object runs as an Actor and has its own thread. This way a polling solution is made.

Links

• https://os.mbed.com/users/Padman/code/MIDIparser/

  This is a partial midi parser.

• http://www.ccarh.org/courses/253/handout/smf/

  The MIDI format explained.

• http://www.personal.kent.edu/~sbirch/Music_Production/MP-II/MIDI/an_introduction_to_midi_contents.htm

  Another MIDI format description.

• https://tttapa.github.io/Arduino/MIDI/Chap00-Arduino-MIDI.html

  A Arduino Midi project with Midi, hardware and software description.

• https://github.com/ncu571633/midi_parser

  A parser for iostream, not suited for mbed-os.

• https://github.com/craigsapp/midifile

  A parser for iostream. This parser is interessing for the analysis of a midi file. One of the exampes dumps a complete midi bestand into readable text.

• https://github.com/ARMmbed/mbed-os-example-filesystem.git

  A mbed-os example that reads the sd card.