1. Lab 3 General MIDI Explorer with Record/Playback
Getting Started
updated 11/08 by Felipe Vilas-Boas
and W. Burleson

2. Where are we? Lab 0 MIDI Receiver Lab 1 Cache Simulator in C
Verilog/Quartus, Breadboarding, GoLogic, MIDI-Ox
Lab 1 Cache Simulator in C
C programming, data structures
Cache architecture and analysis
Lab 2 Pipelined Machine
Pipeline architecture and analysis
Lab 3 General MIDI Explorer with Record/Playback
Microcontroller programming C
Assembly

3. Objectives Exposure to microcontroller programming
Assembly Language (ASM)
Talking to A/D converter
Talking to Timer
Talking to UART
Compiled Language (C)
Data Structure in Memory
Continuation of MIDI theme
Serial communication
Notes and instruments
FUN! A complete system with input, output, storage

4. Requirements C Program ASM Program Send & Receive MIDI Messages
Play and Recording Modes
Store and Replay MIDI Messages
ASM Program
Vary speed of messages via hex switch
Instrument / Note / Velocity via photo cells
Change channels between Percussion & Instrument

5. Relevant AVR Components
C Program
Data EEPROM (Storage)
USART (Communication)
ASM Program
Timer1 (Counter)
ADC (Analog to Digital Converter)
Will manipulate these components using AVR assembly.

6. AVR Assembly Commands similar to MIPS
ldi, breq, andi, lsr, rsr, etc.
‘in’/’out’ used when working with I/O ports
Can ‘rjmp’ using tags (no offsets to worry about)
There are some differences though…
sbic, neg, cbi, etc.

7. Setup Example (AVR) Setup Example
.include "m32def.inc“ (Include system file)
.def Temp=R16 (Define R16 register)
.org 0x (Where to begin)          rjmp RESET (Jump to RESET)
RESET: …

8. Stack Pointer
You must initialize the stack pointer if you wish to return from jumps…
Set stack pointer        
ldi        Temp, 0x65         out        SPL, Temp

9. Setup Example (C) Setup Example
#include <avr/io.h> (Include system file)
int main() {
int data;
DDRA = 0xFF; (PORTA output)
DDRB = 0x00; (PORTB input)
PORTA = 0x55; (Output 0x55 or b )
data = PINB; (Store input values) } …

10. Timer1 Timer1 is the 16-bit counter on the AVR
Will count overflows of Timer1 in order to gauge transmission time.
Good to set counter prescalar to 1024
Choose 1024 prescalar for Timer1
ldi        Temp, 0x05
out        TCCR1B, Temp

11. USART Must initialize with desired baud rate and frame format
Must be initialized in both C and ASM
MIDI Baud rate : kbps
Want start/stop bits and 8 data bits
Read data sheet

12. ADC General AVR ADC reading process: Enable ADC Specify pin to read
Call for conversion
Check completion bit
Copy data to intermediate register

13. Photo

14. MIDI Message Format STATUS / NOTE / VELOCITY
For Note on : 0x90 / 0x?? / 0x??
For Note off : 0x80 / 0x?? / 0x??
For Inst. Change : 0xC0 / 0x??
For Note on Perc. Chan : 0x99 / 0x?? / 0x??
Max data value for MIDI NOTE / VEL should be 0x7F
ADC can output up to 0xFF

15. What Now?
Every time Timer1 overflows, a flag will be triggered. Use this to time transmission.
Package MIDI messages correctly
Three Byte Clusters (Status/Note/Velocity)
MIDI On and Off Messages

16. Hints Datasheet is extremely helpful Timer in ASM can be tricky
Both C and ASM
Timer in ASM can be tricky
Send Dummy Messages to test timing
C program slightly simpler
Start with C to understand the AVR
ASM can be broken into two pieces