Module protocol 

Pure protocol layer: frame construction and parsing. No I/O.

Everything here is a deterministic function of its inputs, which is what makes the wire format unit-testable byte-for-byte (see tests/vectors.rs, whose expected bytes are hand-derived from the DFRobot protocol documentation and an independent CRC-8/MAXIM implementation).

Out-of-range drive values are clamped, not rejected — a setpoint that is merely too large should saturate the wheel, never wrap it around to full reverse. This is part of the crate’s API contract.

Enums

ReplyKind

Which command elicited a telemetry reply — and therefore how its bytes 6–7 must be decoded.

Constants

BAUD

RS485 baud rate. The format is fixed: 115200 8N1, half-duplex.

BRAKE_BYTE

Brake byte value: in velocity mode, 0xFF in byte 7 engages the electric brake.

CMD_DRIVE

Drive command: the 16-bit value is interpreted per the active Mode.

CMD_HZ_MAX

Maximum command rate the motor accepts (Hz).

CMD_MODE

Mode-switch command. Its last byte is the mode, not a CRC.

CMD_QUERY

Feedback query command: the motor replies with a telemetry frame.

CUR_FULL_SCALE_A

Full-scale torque current in amps, at CUR_MAX (and −CUR_MAX).

CUR_MAX

Maximum current command; maps to roughly +8 A.

CUR_MIN

Minimum current command; maps to roughly −8 A.

DRIVE_HZ_MIN

Minimum drive-frame repetition rate (Hz) that sustains motion.

FRAME_LEN

Every frame on the bus, in both directions, is exactly this long.

POS_MAX

Maximum position command; 0..=32767 maps to 0°..360°.

RPM_MAX

Maximum velocity command, RPM.

RPM_MIN

Minimum velocity command, RPM.

Functions

amps_to_raw

Amps → raw current setpoint, clamped to CUR_MIN..=CUR_MAX.

crc8_maxim

CRC-8/MAXIM (Dallas 1-Wire): polynomial x⁸+x⁵+x⁴+1, reflected (0x8C), init 0.

deg_to_raw

Degrees → raw position setpoint, clamped to 0..=POS_MAX.

deg_to_raw8

Degrees → raw 8-bit position, clamped to 0..=255, as carried in byte 7 of a ReplyKind::Query reply.

drive_floor

The longest a wheel may go between drive frames before it coasts: the period of the DRIVE_HZ_MIN floor. A periodic control loop’s cycle must not exceed this, or every cycle the motor slips below the floor and coasts a little.

frame_brake

Electric-brake frame (velocity mode only): value 0 with BRAKE_BYTE in the brake position.

frame_current

Current drive frame. value is clamped to CUR_MIN..=CUR_MAX (±32767, roughly −8 A..+8 A).

frame_drive_reply

Encode a synthetic drive-layout reply frame (the layout elicited by a CMD_DRIVE / 0x64 frame or the broadcast ID query): the encode-side inverse of parse_feedback for ReplyKind::Drive.

frame_feedback

Feedback query frame: the addressed motor replies with telemetry.

frame_from_bytes

Build a Frame from raw bytes: 9 bytes get a CRC-8/MAXIM appended, 10 bytes pass through untouched (byte 9 is not recomputed, so this can send deliberately corrupt frames).

frame_id_query

Broadcast ID-query frame (fixed bytes C8 64 00×7 DE). Any motor on the bus answers with a frame starting with its own ID.

frame_mode

Mode-switch frame. The last byte is the mode value, not a CRC — this is the protocol’s one deliberate deviation from the standard frame shape. Must be sent five times (M0601::set_mode does so).

frame_position

Position drive frame. raw is clamped to 0..=POS_MAX (0°..360°).

frame_query_reply

Encode a synthetic query-layout reply frame (the layout elicited by a CMD_QUERY / 0x74 request): the encode-side inverse of parse_feedback for ReplyKind::Query.

frame_set_id

Set-ID frame (AA 55 53 <new_id> 00×6, no CRC). Persistent; must be sent five times with only one motor on the bus (Bus::set_id handles both).

frame_time

Time on the wire for one FRAME_LEN-byte frame at BAUD — 8N1 sends 10 bits per byte (1 start + 8 data + 1 stop). This is the unit every bus-occupancy budget is built from (see crate::bus::bus_period); the same wire time that sizes DEFAULT_MIN_GAP.

frame_velocity

Velocity drive frame. rpm is clamped to RPM_MIN..=RPM_MAX.

parse_feedback

Parse a telemetry frame from raw reply bytes, decoding bytes 6–7 according to kind — see ReplyKind for why the caller must know which command the reply answers.

parse_feedback_strict

Like parse_feedback, but rejects a frame whose byte 9 does not match its CRC-8/MAXIM: a decoded Feedback with crc_ok == false becomes None.

raw8_to_deg

8-bit position → degrees (raw × 360 / 255), as carried by a ReplyKind::Query reply.

raw_to_amps

Raw current value → amps (raw × 8 / 32767).

raw_to_deg

16-bit position → degrees (raw × 360 / 32767), as carried by a ReplyKind::Drive reply.

validate_id

Check that id is an assignable motor ID (0x01..=0xFE).

Type Aliases

Frame

A complete 10-byte bus frame.