Brushed Motor Controller (BMC)

Drives a brushed DC motor with closed-loop position or velocity control, quadrature encoder feedback, limit switches and current sensing. Firmware lives in src/bmc.

This is the most complex board in the tree and the only one that runs a control loop. For background on the motors themselves see Brushed DC Motors.

Hardware

Interface	Peripheral	Notes
H-bridge	htim1 PWM + direction GPIO	motor output
Quadrature encoder	htim4 in encoder mode	position and velocity feedback
Limit switches A and B	GPIO	presence and polarity are configurable
Current sense	ADC1 via AD8418A	published as current
CAN	FDCAN1
Logging	LPUART1 (DMA)

Behavior

Timer	Rate	Purpose
htim17	25 Hz	control loop update
htim6	10 Hz	publish BMCMotorState
htim16	10 Hz	CAN watchdog
htim2	-	elapsed-time source for PID and encoder timing

Modes

The board is a small state machine, selected by BMCModeCmd:

Mode	Value	Behavior
STOPPED	0	output disabled
FAULT	1	latched error; output disabled until reset
THROTTLE	5	open loop, target is a duty cycle
POSITION	6	closed loop on encoder position
VELOCITY	7	closed loop on encoder velocity

Position and velocity modes each load their own PIDF gains from configuration when entered, so the two loops are tuned independently.

Watchdog

A CAN watchdog runs at 10 Hz. If commands stop arriving the board faults with WWDG_EXPIRED and disables the output, so a lost link or a crashed host stops the motor rather than leaving it running at its last command.

Calibration

Position control requires a known reference. The board tracks an uncalibrated position until a limit switch establishes the offset; commanding position or velocity before that faults with UNCALIBRATED. Each limit switch can be configured as forward or backward, and can optionally readjust the position estimate when hit.

Fault Codes

Published in BMCMotorState.fault_code:

Code	Meaning
NONE	no error
NO_MODE	no mode selected
INVALID_CONFIGURATION_FOR_MODE	closed-loop mode requested with no feedback configured
INVALID_FLASH_CONFIG	configuration in flash is not usable
WWDG_EXPIRED	CAN watchdog timed out
UNCALIBRATED	position or velocity commanded before calibration
CAN_ERROR_FATAL	unrecoverable CAN error
I2C_ERROR_FATAL	unrecoverable I2C error
SPI_ERROR_FATAL	unrecoverable SPI error

Clear a latched fault with BMCResetCmd.

CAN Interface

Receives

Message	Base ID	DLC	Signals
BMCModeCmd	0x80100000	2	mode (8), enable (1)
BMCTargetCmd	0x80110000	5	target (32, signed), target_valid (1)
BMCResetCmd	0x80120000	1	reset, clear_faults
ESWConfigCmd	0x80F00000	6	address, value, apply
ESWProbe	0x80F10000	4	data

Sends

Message	Base ID	DLC	Signals
BMCMotorState	0x80130000	16	mode (8), fault_code (8), position (32, signed), velocity (32, signed), current (32, signed), limit_a (1), limit_b (1), is_stalled (1)
ESWAck	0x80F20000	4	data

target is interpreted according to the active mode: duty cycle in throttle, position in position mode, velocity in velocity mode. target_valid must be set for the command to take effect.

Configuration

Definition: config/bmc.yaml, the largest in the tree at 84 bytes. Device values live under rover/ra/, rover/sp/, rover/cm/ and rover/test/.

Register	Type	Meaning
can_id	uint8	this board’s CAN node ID
host_can_id	uint8	where to address published state
sys_cfg	uint8	motor_en, motor_inv, quad_en, quad_phase, stall_en, lim_a_present, lim_b_present
limit_cfg	uint8	per switch: en, active_high, is_forward, use_readjust for A (bits 0-3) and B (bits 4-7)
quad_cpr	float32	encoder counts per revolution
gear_ratio	float32	motor to output gear ratio
rotor_output_ratio	float32	rotor to output ratio
limit_a_position	float32	position asserted when limit A is hit
limit_b_position	float32	position asserted when limit B is hit
max_pwm	float32	output ceiling
min_pos, max_pos	float32	software position limits
min_vel, max_vel	float32	software velocity limits
pos_k_p, pos_k_i, pos_k_d, pos_k_f	float32	position loop PIDF gains
vel_k_p, vel_k_i, vel_k_d, vel_k_f	float32	velocity loop PIDF gains
stall_current	float32	current above which is_stalled is asserted
delta_position	float32	position change threshold used in stall detection

See Register Definitions and CAN Configuration Interface.

Building

./scripts/build.sh --src src/bmc --preset Debug
./scripts/build.sh --src src/bmc --preset Debug --flash

src/bmc is in ci.json, so CI builds it at both presets.

Related Scripts

Both have hardcoded CAN IDs and interfaces, so read them before running:

• tools/scripts/restart_bmc.py sends BMCResetCmd to node 49 on can1.
• tools/scripts/send_can.py drives node 0x67 on can0 to a fixed target at 20 Hz.