AVR Embedded Control System

Register-level ATmega32 firmware spanning external interrupts, hardware timers, matrix keypad input, SRAM buffering, ADC temperature sensing, PWM generation, and servo control — written in AVR assembly and C, with no HAL or abstraction layer.

Reconstructed and corrected from completed ATmega32/STK500 laboratory experiments and surviving project materials.

Labs

#	Module	Key techniques	Lang
6	External Interrupts	INT0/INT1/INT2 vector table, fixed hardware priority, SREG + full register save/restore in every ISR	asm
7	Timers & Keypad	Timer0 normal mode (prescaler 1024), TCNT0 preload math, 4×4 matrix keypad scan, ASCII multi-tap lookup table, 64-byte SRAM message buffer, live delay adjustment via interrupts	asm
8	PWM & ADC	Fast PWM on OC0, 7-position servo control, free-running ADC, LM34 temperature sensor, temperature-band-to-angle mapping	asm + C

Each lab folder has its own README.md with wiring diagrams, register-level math, build steps, and a changelog versus the original experiment.

Technical highlights

• Direct peripheral control — every peripheral (timer, ADC, interrupt controller, PWM) configured by writing named bit fields into I/O registers; no libraries involved
• Interrupt-driven timing — Lab 7 Part 3 adjusts inter-character playback delay live (0.5 s – 5 s) via INT0/INT1 while a message plays back from SRAM
• Correct ISR discipline — all ISRs push and restore SREG plus every clobbered register; nested interrupt edge cases documented
• Derived timing constants — TCNT0 preloads and OCR0 compare values calculated from first principles ((OCR0+1) × 64 µs at 1 MHz / prescaler 64), then verified empirically against the actual hardware
• Boundary conditions guarded — SRAM buffer rejects input past 64 bytes; # with an empty buffer is ignored rather than reading uninitialized memory

Hardware

Part	Role
ATmega32A	Target MCU
STK500	Development board — LEDs on PORTA/PORTB, switches on PORTD
JTAGICE mkII	On-chip debugger and programmer
4×4 matrix keypad	Input for Labs 7 and 8
Hobby servo	Output actuator for Lab 8
LM34 temperature sensor	ADC input (PA0) for Lab 8 Part 6

Build

Atmel Studio 7 / Microchip Studio

1. New Project → AVR Assembler (or GCC C Executable) → device ATmega32
2. Add the relevant source file from the lab folder
3. Lab 7 only: set PART_SELECT to 1, 2, or 3 near the top of the file
4. Build → F7, then Tools → Device Programming → JTAGICE mkII → Program Flash

Command line

avra -I /usr/share/avra Lab6_Interrupts/lab6_interrupts.asm
avra -I /usr/share/avra Lab7_Timers_Keypad/lab7_timers_keypad.asm
avr-gcc -mmcu=atmega32 -DF_CPU=1000000UL -Wall -Wextra -Os \
  -c Lab8_PWM_ADC/lab8_part6_adc_servo.c

CI assembles and compiles every source file (all three PART_SELECT configurations for Lab 7) on every push — green badge above means everything builds clean.

Clock

All timing constants assume 1 MHz (ATmega32 default internal RC fuse setting). Scale delay-loop counts and timer preloads by 8 if running at 8 MHz, or set the CLKDIV8 fuse to stay at 1 MHz.