Author: Kiran Gunathilaka · Target MCU: ATmega32U4 @ 16 MHz · Firmware language: C (AVR-GCC)
This firmware delivers real-time motion control, sensing, and safety for the autonomous mobile robot (AMR). It runs solely on the ATmega32U4 board—all Jetson-side logic lives elsewhere.
| Area | Key Points |
|---|---|
| Motion Control | Dual NEMA-24 stepper drivers (STEP/DIR), trapezoidal profile generator, 50 Hz update loop |
| Odometry | Mixed INT + PCINT quadrature decoding (32-bit counters), forward & yaw estimation |
| IMU | BNO055 low-level driver, health watchdog with soft/hard reset, Euler + gyro + accel feed |
| ADC | Dual battery rails + three cliff sensors, software averaging, mV conversion |
| Timing | 64-bit, 1 µs global clock (Timer-0), dedicated timers for both motors + main loop |
| Comms | USB-CDC, binary command & telemetry packets, CRC-16, ≈ 50 Hz upstream |
| Safety | 200 ms command-loss stop, emergency GPIO, IMU watchdog, brown-out fuse ready |
| Function | Arduino Label | AVR Pin | Notes |
|---|---|---|---|
| LEFT PUL | D5 | PC6 / OC3A | Timer-3 toggle |
| LEFT DIR | D12 | PD6 | Forward / Reverse |
| LEFT ENA | D10 | PB6 | Active-HIGH (inverted logic) |
| RIGHT PUL | D9 | PB5 / OC1A | Timer-1 toggle |
| RIGHT DIR | D8 | PB4 | Forward / Reverse |
| RIGHT ENA | D6 | PD7 | Active-HIGH |
| ENC L A | D1 | PD2 / INT2 | |
| ENC L B | D0 | PD3 / INT3 | |
| ENC R B | D7 | PE6 / INT6 | |
| ENC R A | D8 | PB4 / PCINT4 | |
| EMERGENCY | D11 | PB7 / PCINT7 | Active-LOW |
| BNO055 RST | — | PF7 | Pull HIGH for reset |
| ADC | PF0, PF1, PF4-6 | — | VBAT & cliff sensors |
| Timer | Mode / Prescale | Purpose | Source File |
|---|---|---|---|
| Timer-0 (8-bit) | Free-running, ÷8 → 0.5 µs/tick | 64-bit microsecond clock | systime.c |
| Timer-1 (16-bit) | CTC, OC1A toggle, ÷1024 | RIGHT motor STEP (PB5) | motors.c |
| Timer-3 (16-bit) | CTC, OC3A toggle, ÷1024 | LEFT motor STEP (PC6) | motors.c |
| Timer-4 (10-bit enhanced) | CTC, OCR4A = 156, ÷1024 | 100 Hz main loop interrupt | main.c |
| TWI (I²C) | 100 kHz | BNO055 IMU | bno055_ll.c |
| Value | Meaning |
|---|---|
0 – AUTONOMOUS |
MCU executes pre-planned trapezoidal profiles sent from host |
1 – TELEOPERATOR |
Host sends discrete f/b/l/r bits; MCU handles acceleration & braking |
| Value | Description |
|---|---|
0 – DEBUG_OFF |
No extra serial output |
1 – MOTION_DEBUG |
Streams wheel speeds, odom, etc. |
2 – RX_ECHO |
Echo raw command packets |
3 – MD_AND_ECHO |
Combine 1 + 2 |
The tele-operator logic is a compact Mealy machine with four states and four primary transitions:
NONETELEOP→ no active commandACCELERATING→ ramp up to target speed/profileCONSTANT→ cruise at steady velocityDECELERATING→ brake to a smooth stop
Each new key-press combination (f b l r) triggers a transition. The handler decides whether to regenerate a fresh profile or decelerate gently before accepting the next command—keeping ride smooth and preventing stepper stalls.
Defines clocks, prescalers, all pin macros, wheel geometry, and motion constants. Central point for hardware adaptation—no magic numbers outside this file.
Initialises every subsystem, arms Timer-4 for 100 Hz scheduling, parses USB packets, executes the Mealy machine, and pushes telemetry. Keeps application logic separate from drivers.
Pure-C driver for two stepper modules:
- Direction bits + enable gating
- Speed-to-frequency helper converts mm/s → timer TOP
- Independent timers let wheels spin at arbitrary RPMs while MCU remains free.
Robust 4-channel quadrature decoder:
- INT2/INT3 (left) + INT6/PCINT4 (right)
- Emergency button multiplexed on PCINT0 ISR
- Computes Δticks, mm/s, deg/s and integrates distance/heading.
Motion planner providing dual Profile instances (linear + angular). Implements a trapezoidal/triangular ramp with automatic braking-distance check. Feeds velocity/omega to motors_update().
Implements 64-bit microsecond counter via Timer-0 overflow; utility micros64() is used everywhere timing matters.
ADC multiplexer, 4-sample software average, milli-volt conversion using configurable divider ratios.
Bare-metal I²C driver plus convenience wrappers; watchdog function initiates graceful soft reset and GPIO hard reset if the sensor becomes unresponsive for > 300 ms.
Minimal CDC-ACM wrapper; DMA-less TX buffer ensures predictable latency at 115 200 Bd.
- Commands: structured binary with CRC-16 (see
serial_format.h). - Telemetry: fixed-width ASCII line for easy logging/plotting & optional debug fields.
- Command-loss watchdog: disables steppers after 200 ms silence.
- Emergency button: hardware-level pull-down on PB7 triggers immediate
motors_stop_all(). - IMU Watchdog: toggles between soft and hard reset based on failure duration.
Change only include/config.h when migrating to a new chassis:
- Update pin macros, wheel diameter/base, encoder PPR & gear ratio.
- Tweak trapezoid limits (
TELEOP_SPEED,TELEOP_ACC, etc.).
No other file should require edits—one-file re-target by design.
- Single-responsibility drivers—each peripheral lives in its own
.c/.hpair. - Interrupt isolation: ISRs are kept minimal; heavy math runs in the main thread.
- All maths use
float, but critical timing uses integer TOP calculations to keep ISR jitter low. - Consistent naming conventions and exhaustive
static inlinehelpers promote readability.
Released under the MIT License.
For questions, open an issue or email kiran.gunathilaka [at] example.com.
All the locations are respect to my machine. change accordingly
C:\Users\META\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino17/bin/avrdude.exe -C"C:\Users\META\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino17/etc/avrdude.conf" -v -V -patmega32u4 -cavr109 "-PCOM14" -b57600 -D -Uflash:w:"D:\Downloads\AMR\GithubOrg\lower_layer_controller\avr_controller\Debug\avr_controller.hex":i