mc_stepper_driver

Low level communication drivers for the stepper motor controller board running the mc_stepper firmware.

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Table of Contents

• mc_stepper_driver
  • 1 Overview
  • 2 CAN Bus Drivers
  • 3 CAN Bus Messages
    • 3.1 Message Table
    • 3.2 Muxed Setpoint (command_stepper)

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1 Overview

CAN drivers are included in the mc_stepper_driver.h file for simple implementation.

This repository defines the CAN protocol contract for MC Stepper: message IDs, DLCs, signal layouts and scaling. The source of truth is the DBC file: can_mc_stepper.dbc.

Note: Behavioural semantics (controls state machine, safety gating of config commands, telemetry rates, fault handling) are owned by the mc_stepper firmware and are documented there.

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2 CAN Bus Drivers

CAN drivers are implemented via the can_driver submodule.

All CAN IDs follow the ScalpelSpace node CAN ID standard defined by can_driver: the 11-bit classic CAN ID is split into a 6-bit message_id and a 5-bit node_id, so a node's on-bus ID is its base message ID plus its assigned node ID. Node IDs 0 (unassigned) and 31 (broadcast) are reserved, and node IDs are assigned at runtime via the dynamic allocation protocol.

See the can_driver README for the full ID scheme, reserved ID ranges and the node ID allocation protocol.

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3 CAN Bus Messages

3.1 Message Table

Direction is from the MC Stepper node's perspective: TX = transmitted by MC Stepper, RX = received by MC Stepper.

Base ID (hex)	Message	DLC	Direction	Description
0x20	state	5	TX	Periodic system state, MCU temperature, fault byte and TMC2209 status.
0x40	stallguard_event	5	TX	Event frame on StallGuard stall detection edge.
0x60	command_stepper	6	RX	Control mode, enable, clear faults and muxed setpoint (see 3.2 Muxed Setpoint (command_stepper)).
0x80	command_stepper_zero	1	RX	Software zero of the position reference.
0xA0	sensor	6	TX	Encoder raw count and unwrapped position (rad).
0xC0	controls_diagnostic	8	TX	Control loop internals: setpoints, position error and step rate command.
0xE0	motion_config_set	7	RX	Set microstep size, max acceleration and max velocity.
0x100	motion_config_get	1	RX	Request motion configuration.
0x120	motion_config_response	6	TX	Response to motion_config_get.
0x140	current_config_set	6	RX	Set run current (mA) and IRUN/IHOLD/IHOLDDELAY scalers.
0x160	current_config_get	1	RX	Request current configuration.
0x180	current_config_response	5	TX	Response to current_config_get.
0x1A0	controls_config_set	8	RX	Set closed loop PID gains.
0x1C0	controls_config_get	1	RX	Request PID gains.
0x1E0	controls_config_response	6	TX	Response to controls_config_get.
0x200	stallguard_set	3	RX	Enable StallGuard detection and set SGTHRS threshold.
0x220	stallguard_get	1	RX	Request StallGuard status.
0x240	stallguard_response	5	TX	Response to stallguard_get: config, SG_RESULT and stalled flag.
0x260	datetime_set	7	RX	Set the RTC date and time.
0x280	datetime_get	0	RX	Request the RTC date and time.
0x2A0	datetime_response	7	TX	Response to datetime_get.
0x2C0	rgb_led_set	3	RX	Set the on-board RGB LED colour.
0x3C0	version_get	0	RX	Request the firmware version.
0x3E0	version_response	4	TX	Response to version_get: major, minor, patch and identifier.

3.2 Muxed Setpoint (command_stepper)

command_stepper carries a single 32-bit setpoint field (bytes 2..5) multiplexed by the control_mode signal:

control_mode	Active setpoint signal	Unit
1	target_position_abs	rad
2	target_velocity	rad/s
3	target_position_rel	rad
4	target_position_ol	rad

All setpoint signals are signed 32-bit with 0.001 scaling. A control_mode of 0 (or any unlisted value) carries no setpoint, allowing frames that only toggle enable or clear_faults.