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.

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.