Arnie

Firmware for Arnie, a differential-drive mobile robot built around an STM32F103C8T6 (Blue Pill). The robot senses its surroundings with a Delta-2B rotating laser radar, finds its heading with a GY-271 magnetometer, drives two brushed DC motors through a custom H-bridge (2× IR2184 per motor) and closes the loop with ×4 quadrature wheel encoders. Every activity runs as a task under the AcroSched cooperative scheduler.

Highlights

• MCU — STM32F103C8T6 (Cortex-M3), 72 MHz from an 8 MHz HSE (PLL ×9); APB1 = 36 MHz, APB2 = 72 MHz. Fits the 64 KB Flash / 20 KB RAM budget.
• Dual toolchain — builds clean under Arm Compiler 6 and GCC (arm-none-eabi) through the CMSIS-Toolbox; toolchain-specific options are isolated in for-compiler blocks.
• No libm — transcendental maths (heading arctangent) is approximated in-tree, so the image stays small and link-order independent.
• Static memory only — no malloc/free anywhere.
• Cooperative-safe drivers — every bus wait is bounded by a timeout; a stuck peripheral raises a fault flag instead of hanging the dispatcher.
• Portable BSP — bsp/bsp.c is the only board-specific file; drivers include bsp.h and never touch an MCU register directly.

Hardware

Subsystem	Interface	Pins	Timer / DMA
Lidar (Delta-2B)	USART1 RX, 230400 8N1, simplex	PA10 (RX, 5 V tolerant)	DMA1 Ch5
Magnetometer	I2C1, 100 kHz	PB6 SCL, PB7 SDA	polled
Motor A	TIM1 PWM ~20 kHz	PA8 / PA11, SD PB12	TIM1_CH1/CH4
Motor B	TIM4 PWM ~20 kHz	PB8 / PB9, SD PB14	TIM4_CH3/CH4
Encoder A	×4 quadrature	PA0 / PA1	TIM2
Encoder B	×4 quadrature	PA6 / PA7	TIM3
Debug console	USART2 TX, 115200 8N1	PA2	—
LED	GPIO (active-low)	PC13	—

The magnetometer driver auto-detects the chip: it probes an HMC5883L at 0x1E, then a QMC5883L-class clone (e.g. "HA5883") at 0x0D, and configures whichever answers.

Software architecture

• Scheduler — AcroSched is linked as a per-compiler prebuilt library (lib/stm32f1-ac6/acrosched.lib, lib/stm32f1-gcc/libacrosched.a); its headers are vendored in lib/inc/. Start-up order is bspStart() → acroInit(&sys_tick) → acroAddTask(...) → acroRun().
• Timebase — a 1 ms SysTick increments a BSP-owned tick counter used as the scheduler time source. SystemInit() configures clocks, GPIO and the USARTs before main(); it does not enable SysTick or interrupts — bspStart() does that.
• Drivers — lidar, compass, motor, encoder under navigation/, each exposing a non-blocking *Process() entry that does one bounded unit of work per dispatcher visit.

Repository layout

app/            application entry point and tasks (main.c, syscalls.c)
bsp/            board support package (only platform-specific code)
navigation/     drivers: lidar, compass, motor, encoder
lib/            AcroSched prebuilt libraries + vendored headers
arnie.*.yml     CMSIS-Toolbox solution / project files
HISTORY.md      milestone log of decisions and changes
requirements.md functional / non-functional requirements (REQ-NNN)

Building

The project uses the CMSIS-Toolbox (cbuild):

cbuild arnie.csolution.yml --rebuild

Both Debug and Release contexts build for the STM32F103C8 target under each configured toolchain.

Flashing

With a CMSIS-DAP / ST-Link probe and pyOCD:

pyocd flash -t stm32f103c8 --erase chip .\out\navigation\STM32F103C8\Debug\navigation.hex

Status

Lidar acquisition, the magnetometer (auto-detect HMC/QMC), the cooperative runtime and the dual-toolchain build are working. Motor and encoder drivers are implemented and compile-time gated (MOTOR_ENABLED / ENCODER_ENABLED in app/main.c) while the hardware is wired. Closed-loop speed control, magnetometer calibration, obstacle-avoidance navigation and the independent watchdog are planned (see requirements.md, REQ-013 onward).

License

See LICENSE.