Reference — bus extender

The MUXEN devices this box publishes

Device	Function	Instance	What it carries
Bus extender	31	configured (InstanceNum)	the repeating function itself: running state, and the label given to CAN 1
Generic I/O	17	configured (InstanceNum)	the box's own relays, dry-contact inputs and analog inputs

Both are announced on both segments, so the box is visible and configurable from either side.

MQTT topics on the Brain follow device/<function>/<instance>/<frame>. In practice you will see:

Topic	When
device/17/<n>/life	the box's own I/O, once EnGenIo is set to 1
device/31/<n>/boot, device/17/<n>/boot	at every startup
device/31/<n>/uid, device/17/<n>/uid	in answer to a scan

The extender's own status frame is broadcast on the CAN bus but is not currently published as an MQTT topic by the Brain.

Parameters — bus extender (function 31)

Parameter	Type	Default	Meaning
InstanceNum	0…62	255	the extender's own instance; 255 means not addressed
CanBus1Area	0…255	0	a label for the segment on CAN 1, reported in the box's status frame. Purely informational
CanBus2Area	0…255	1	a label for the segment on CAN 2. Stored, and not used by anything today
ProductId, HardwareId, SoftwareId, SoftwareVersion	read-only		see Reference

Neither label changes what the box does. They exist to record which segment is which; nothing on the boat reads them yet.

A change to InstanceNum takes effect at the next restart — write it with --reboot.

Parameters — generic I/O (function 17)

Parameter	Default	Meaning
InstanceNum	255	the I/O device's instance
EnGenIo	0	publish the inputs, relays and analog inputs
EnAnalogPwr	1	power the analog sensor supply

EnCanAuxPwr is not present on this firmware, and nothing about the second CAN interface needs configuring.

What crosses between the segments

Repeated	every frame received on either segment, in both directions: extended and standard identifiers, data frames and requests for data, whatever the content
Filtering	none. The box does not inspect, select, rate-limit or rewrite anything
Not repeated	configuration traffic addressed to this box's own two devices — it is answered on the segment it arrived on
Not repeated	bus errors and bus-off state. Each segment has its own interface; a fault on one does not put the other in fault
Emitted on both segments	the box's own startup and status frames
Answered on one segment	a reply to a request goes back out on the segment the request came from
Order	frames going one way keep their order; the relative order of frames arriving from opposite segments is not preserved

Timings and buffers

Frames buffered per direction	64; the excess is dropped silently
Generic I/O published	on change, and at least every 500 ms
Extender status frame	every second
Repeating starts	at startup, before any instance number is set

Routines

Routine	Payload	Effect
locate		blinks the system LED for 5 seconds, so the box can be identified physically
reset parameters	0001	restore the instance number to its default
reset parameters	any bit above bit 0	restore every other parameter of that device

muxen-uds -i can0 -F 31 -I <n> locate

LED codes

The common ones only — 1 Hz is running normally, see Reference. This application adds one:

Rate	Meaning
≈5 Hz for 5 seconds	answering a locate request

Limits

Segments joined	2, by one box
Speed, both segments	500 kbit/s, fixed in the firmware
Terminations required	2 per segment — 4 in total
Combined bus load	that of one 500 kbit/s MUXEN bus, shared by both segments
Instance numbers	0…62
Extenders between one pair of segments	1. Loops are not detected

Versions

Hardware	Version	Image
CanCan v1	5.1	010010032-app_bus_extender-firmware.srec
CanCan v2	6.2	010010032-V2-app_bus_extender-firmware.srec

Source: workspace/muxen/cancan/app_bus_extender/, product overlay boards/arm/<board>/010010032.overlay.