Merge branch 'midi_output'

midi_test.c

+//
+// midi_test.c
+// based on hello.ftdi.44.echo.c
+//
+// 115200 baud FTDI MIDI controller
+//
+// set lfuse to 0x5E for 20 MHz xtal
+//
+// Neil Gershenfeld
+// 12/8/10
+// Erik Strand
+// 11/13/2018
+//
+// (c) Massachusetts Institute of Technology 2010
+// This work may be reproduced, modified, distributed,
+// performed, and displayed for any purpose. Copyright is
+// retained and must be preserved. The work is provided
+// as is; no warranty is provided, and users accept all 
+// liability.
+//
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/pgmspace.h>
+
+#define output(directions,pin) (directions |= pin) // set port direction for output
+#define set(port,pin) (port |= pin) // set port pin
+#define clear(port,pin) (port &= (~pin)) // clear port pin
+#define pin_test(pins,pin) (pins & pin) // test for port pin
+#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set
+#define bit_delay_time 8.4 // bit delay for 115200 with overhead
+#define bit_delay() _delay_us(bit_delay_time) // RS232 bit delay
+#define half_bit_delay() _delay_us(bit_delay_time/2) // RS232 half bit delay
+#define char_delay() _delay_ms(10) // char delay
+
+#define serial_port PORTA
+#define serial_direction DDRA
+#define serial_pins PINA
+#define serial_pin_in (1 << PA0)
+#define serial_pin_out (1 << PA1)
+
+#define led_pin (1 << PB2)
+
+#define note_on 144
+#define note_off 128
+
+
+void put_char(volatile unsigned char *port, unsigned char pin, uint8_t txchar) {
+    // send character in txchar on port pin
+    //    assumes line driver (inverts bits)
+    //
+    // start bit
+    clear(*port,pin);
+    bit_delay();
+
+    // unrolled loop to write data bits
+    if bit_test(txchar,0)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,1)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,2)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,3)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,4)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,5)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,6)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+    if bit_test(txchar,7)
+       set(*port,pin);
+    else
+       clear(*port,pin);
+    bit_delay();
+
+    // stop bit
+    set(*port,pin);
+    bit_delay();
+
+    // char delay
+    char_delay();
+}
+
+struct MidiEvent {
+    uint16_t tick;
+    uint8_t status;
+    uint8_t note;
+    uint8_t velocity;
+};
+
+int main(void) {
+    // Set the clock prescaler to 1.
+    CLKPR = (1 << CLKPCE);
+    CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
+
+    // Set the 8 bit timer's prescaler to 1/1024.
+    TCCR0B |= 0b00000101;
+
+    // Initialize serial output pins
+    set(serial_port, serial_pin_out);
+    output(serial_direction, serial_pin_out);
+
+    // Configure led_pin as an output.
+    DDRB |= led_pin;
+
+    uint16_t current_tick = 0;
+    uint16_t max_tick = 960;
+    uint8_t event_index = 0;
+
+    // 120 ticks per quarter note
+    const struct MidiEvent events[] = {
+        // Bb major 7
+        {0, note_on, 58, 100},
+        {30, note_on, 62, 100},
+        {60, note_on, 65, 100},
+        {90, note_on, 69, 100},
+        {180, note_off, 69, 100},
+        {180, note_off, 65, 100},
+        {180, note_off, 62, 100},
+        {180, note_off, 58, 100},
+
+        // sentinel event
+        {65535, note_off, 50, 100},
+    };
+
+
+    while (1) {
+        if (TCNT0 >= 120) {
+            TCNT0 = 0;
+            ++current_tick;
+
+            while (events[event_index].tick <= current_tick) {
+                put_char(&serial_port, serial_pin_out, events[event_index].status);
+                put_char(&serial_port, serial_pin_out, events[event_index].note);
+                put_char(&serial_port, serial_pin_out, events[event_index].velocity);
+                ++event_index;
+            }
+
+            if (current_tick == max_tick) {
+                current_tick = 0;
+                event_index = 0;
+                PORTB ^= led_pin;
+            }
+        }
+    }
+}
+