Appendix A — AVR and Arduino¶

This appendix is intentionally outside the register-level core. Arduino is neither required nor the reference implementation.

Purpose¶

After learning the MCU directly, map familiar Arduino abstractions back to the ATmega1284P hardware, avr-gcc toolchain and generated AVR instructions.

Mapping table¶

Arduino concept	AVR view
`pinMode()`	DDRx direction bits
`digitalRead()`	PINx input register
`digitalWrite()`	PORTx output/pull-up behavior
`analogRead()`	ADC mux/control/result registers
`analogWrite()` where supported	timer/output-compare PWM
`Serial`	USART registers, baud generator, polling/interrupts
`SPI`	native SPI registers and pins
`Wire`	TWI/I2C peripheral
`delay()`	framework timing facilities
`millis()`	timer interrupt plus software time state
`setup()/loop()`	framework startup plus repeated application control flow

Build stack¶

Treat an Arduino sketch as source entering a larger build/runtime framework. Inspect verbose build output and identify framework code, compiler, assembler, linker, ELF/HEX production and upload/programming tool.

Comparison exercise¶

Implement the same LED/button behavior three ways: direct AVR assembly, direct register-level C, and Arduino API. Disassemble the builds and compare initialization, code size and peripheral configuration.

Serial and timers¶

Compare a minimal direct USART implementation with Serial. Identify hardware versus library policy. Arduino runtime services can own/depend on timers, so determine resource ownership before mixing direct timer programming with framework functions.

Bootloaders¶

An Arduino-style bootloader is one programming approach, not a requirement of AVR. Relate it to Appendix F's ISP, boot-section and fuse discussion.

Goal¶

The learner should be able to use Arduino when convenient while still answering: which AVR peripheral, registers and generated instructions implement this abstraction?