Protocol & Commands

The host and robot speak protocol v2: newline-terminated ASCII lines with sign-prefixed integer arguments. This page is the gist; the authoritative, exhaustive reference is docs/protocol-v2.md and the feature specification.

Wire format

• Serial: 115200 baud, bidirectional over the micro:bit’s USB serial.
• Radio: micro:bit radio group 10. A command relayed over radio carries a > prefix; responses come back with <. This lets the host run wirelessly through a second micro:bit acting as a USB-serial bridge.
• Numbers: every numeric value is sign-prefixed — +1234, -42, +0. No floating point on the wire; fixed-point scaling is used where needed.
• Responses: OK / ERR / EVT / TLM / CFG / ID.

Most-used commands

Command	Format	Description
S	S+LS+RS	Set left/right motor speeds; runs until stopped (sends watchdog keepalives)
T	T+LS+RS+DUR	Drive at speeds for DUR ms
D	D+LS+RS+DIST	Drive at speeds for DIST mm (encoder-based, blocking)
G	G+X+Y+Speed	Arc-navigate to relative XY target; emits G+DONE
X / STOP	X	Stop immediately
ENC	ENC	Query encoder positions → ENC+L+R
EZ	EZ	Zero encoder counts
SO / SZ / SI	—	Query / zero / set dead-reckoning odometry
OP	OP	Query OTOS pose → OP+X+Y+H
LS / CS	—	Read line sensor / color sensor
HELLO	HELLO	Trigger device announcement (DEVICE:+name+version)

Two ways to drive

• Discrete moves — D/T/G are blocking, no watchdog; the host waits for the EVT done event.
• Continuous driving — S runs open-ended; the host must send periodic keepalives. The firmware safety watchdog window is 500 ms by default.

Calibration parameters

Motor scale, PID gains, trackwidth, and navigation tolerances are all set live with K* commands (e.g. KCP, KCI, KTW, KGD). The full table of K parameters, units, and defaults is in the specification.

Don’t hand-roll the protocol

Use the robot_radio host library; it owns the serial port, framing, and command formatting. The layered API (NezhaProtocol → Nezha → sensors/nav) is the supported way to talk to the robot.