test/midi.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include <stdio.h>
   4 #include "midi.h"
   5
   6 volatile int16_t midisync_clocked = 0;
   7
   8 #define MIDI_Q_SIZE 32
   9 volatile uint8_t midi_q[MIDI_Q_SIZE];      // cyclic queue for midi msgs
  10 volatile static uint8_t head_idx = 0;
  11 volatile static uint8_t tail_idx = 0;
  12
  13 #define MIDI_BAUDRATE 31250UL       // the MIDI spec baudrate
  14
  15 // interrupt on receive char
  16 ISR(SIG_USART0_RECV) {
  17         char c = UDR0;
  18
  19         midi_q[tail_idx++] = c;    // place at end of q
  20         tail_idx %= MIDI_Q_SIZE;
  21
  22         if( tail_idx == head_idx ) {
  23                 // i.e. there are too many msgs in the q
  24                 // drop the oldest msg?
  25                 head_idx++;
  26                 head_idx %= MIDI_Q_SIZE;
  27         }
  28 }
  29
  30 void midi_init(void) {
  31         /* setup the MIDI UART */
  32         uint16_t ubbr = (F_CPU / (16 * MIDI_BAUDRATE)) - 1;     // formula in datasheet
  33         UCSR0B |= (1<<RXEN0) | (1<<TXEN0)| (1<<RXCIE0);    // read and write, interrupt on recv.
  34         UBRR0L = (uint8_t)ubbr;               // set baudrate
  35         UBRR0H = (uint8_t)(ubbr>>8);
  36 }
  37
  38 int midi_putchar(uint8_t c) {
  39         loop_until_bit_is_set(UCSR0A, UDRE0);
  40         UDR0 = c;
  41         return 0;
  42 }
  43
  44 int midi_getch(void) {     // checks if there is a character waiting!
  45         if (head_idx != tail_idx)
  46                 return 1;
  47         return 0;
  48 }
  49
  50 int midi_getchar(void) {
  51         char c;
  52
  53         while (head_idx == tail_idx);
  54
  55         cli();
  56         c = midi_q[head_idx++];
  57         head_idx %= MIDI_Q_SIZE;
  58         sei();
  59
  60 //      midi_putchar(c);
  61         return c;
  62 }
  63
  64 static uint8_t SYSEX_snd_checksum;
  65 void sysex_start(uint8_t command) {
  66         // Reset checksum
  67         SYSEX_snd_checksum = 0;
  68
  69         // Send SYSEX start, manufacturer ID, model number and command
  70         midi_putchar(MD_SYSEX_START);
  71         midi_putchar(MD_MF_ID_1);
  72         midi_putchar(MD_MF_ID_2);
  73         midi_putchar(MD_MF_ID_3);
  74         midi_putchar(MD_SYNTH_ID);
  75         midi_putchar(command);
  76 }
  77
  78 void sysex_data(uint8_t data) {
  79         // split one byte of data in two
  80         uint8_t msb = data >> 7;
  81         uint8_t lsb = data & 0x7f;
  82         midi_putchar(msb);
  83         midi_putchar(lsb);
  84
  85         SYSEX_snd_checksum = (SYSEX_snd_checksum + msb + lsb) % 128;
  86 }
  87
  88 void sysex_end(void) {
  89         // Send checksum
  90         midi_putchar(SYSEX_snd_checksum);
  91
  92         // Send end of SYSEX
  93         midi_putchar(MD_SYSEX_END);
  94 }
  95