Add MIDI output test

midi_test.c

+//
+// sampler.c
+// based on hello.ftdi.44.echo.c
+//
+// 115200 baud FTDI character echo, with flash string
+//
+// set lfuse to 0x5E for 20 MHz xtal
+//
+// Neil Gershenfeld
+// 12/8/10
+// Erik Strand
+// 11/6/2018
+//
+// (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 8.5 // 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 input_pin (1 << PA5)
+
+void put_char(volatile unsigned char *port, unsigned char pin, char 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
+   //
+   bit_delay();
+   }
+
+void put_string(volatile unsigned char *port, unsigned char pin, char *str) {
+   //
+   // print a null-terminated string
+   //
+   static int index;
+   index = 0;
+   do {
+      put_char(port, pin, str[index]);
+      ++index;
+      } while (str[index] != 0);
+   }
+
+#define input_pin (1 << PA5)
+
+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;
+
+    // Blink the LED with ~1.0s half-period.
+    // 100 * 200 * 1024 / 20M ~ 2.5s
+    int count = 0;
+    while (1) {
+        // If it's been 10ms, reset the timer and increment count.
+        if (TCNT0 >= 200) {
+            TCNT0 = 0;
+            ++count
+
+            // When count reaches 100, turn the LED on and send a note on command.
+            if (count == 100) {
+                PORTB |= led_pin;
+                put_char(&serial_port, serial_pin_out, 144); // note on
+                put_char(&serial_port, serial_pin_out, 70); // note (A4)
+                put_char(&serial_port, serial_pin_out, 100); // velocity
+            }
+
+            // When count reaches 200, turn the LED off and send a note off command.
+            else if (++count == 200) {
+                PORTB &= ~led_pin;
+                put_char(&serial_port, serial_pin_out, 144); // note off
+                count = 0;
+            }
+        }
+    }
+}
+