1. Robocon 2007 Electronics Quickstart!
Session 2
First Program - GPIO
Prepared by
KI Chi Keung [chikeung＠ust.hk]
WONG Long Sing (Sam) [sam＠hellosam.net]

2. Today’s Timeline Driving the Debug LED Reading a button
Schematic Reading
Special Function Register
ATMega128 Specification Reading
Hexadecimal / Bitwise Operation
Deterministic Speed
Reading a button
Debouncing
State

3. Schematic Reading Identify the Component Identify the Wire / Net Label
Identify the Hardware pin

4. Special Function Register
Identify the hardware module to be used
GPIO?
Timer?
UART?
I2C?
Identify the SFR involved

5. ATMega128 Specification Reading
It’s silly to read all 3xx pages in a single pass. Don’t try to do that.
Only refer to what you need.
Usually SFR description is what you needed.

6. Hexadecimal / Bitwise Operation
0x21  0b
0x43  0b
0xCD  0b
0xFE  0b
_BV(0)  0b
_BV(1)  0b
_BV(7)  0b

7. Deterministic Speed
Each assembly instruction takes defined CPU cycles to run, no more, no less.
Period of CPU cycles depends on your clock
While the clock is fixed now, so each instruction take exactly deterministic speed. This is true if and only if your program solely occupies the CPU.