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MSP Extensions

Cleanflight includes a number of extensions to the MultiWii Serial Protocol (MSP). This document describes those extensions in order that 3rd part tools may identify cleanflight firmware and react appropriately.

MSP_IDENT capabilities

Cleanflight sets a number of non-standard bits in the MSP_IDENT message in order to identify the firmware. For completeness, this includes flags defined for baseflight.

Value	Mnemonic	Notes	Reference
1 << 29	CAP_CLEANFLIGHT_CONFIG	The firmware supports cleanflight configuration options. This is the definitive test for cleanflight firmware	src/main/io/serial_msp.c
1 << 30	CAP_BASEFLIGHT_CONFIG	The firmware supports baseflight configuration options. See the baseflight documentation for details.	src/main/io/serial_msp.c
1 << 31	CAP_PLATFORM_32BIT	This is a 32bit platform.	src/main/io/serial_msp.c

Modes Extension

The cleanflight modes extension to MSP supports the extended auxiliary modes introduced 2014-10-14. The CAP_CLEANFLIGHT_CONFIG capabilities flag should be used to confirm the availability of extended auxiliary modes. If this flag is not present, the legacy MSP MSP_BOX and MSP_SET_BOX messages should be used.

Note: In the following descriptions, the format of the original MSP documentation is followed.

MSP_MODE_RANGES

The MSP_MODE_RANGES returns the current auxiliary mode settings from the flight controller. It should be invoked before any modification is made to the configuration.

The message returns a group of 4 unsigned bytes for each 'slot' available in the flight controller. The number of slots should be calculated from the size of the returned message.

Command	Msg Id	Direction	Data	Type	Notes
MSP_MODE_RANGES	34	to FC	(none)	N/A	Following this command, the FC returns a block of 4 bytes for each auxiliary mode 'slot'

Unassigned slots have rangeStartStep == rangeEndStep. Each element contains the following fields.

Direction	Data	Type	Notes
returned from FC	permanentId	uint8	See Modes.md for a definition of the permanent ids
returned from FC	auxChannelIndex	uint8	The Aux switch number (indexed from 0)
returned from FC	rangeStartStep	uint8	The start value for this element in 'blocks' of 25 where 0 == 900 and 48 == 2100
returned from FC	rangeEndStep	uint8	The end value for this element in 'blocks' of 25 where 0 == 900 and 48 == 2100

Thus, for a cleanflight firmware with 40 slots for auxiliary settings, 160 bytes would be returned in response to MSP_MODE_RANGES,

MSP_SET_MODE_RANGE

The MSP_SET_MODE_RANGE is used to inform the flight controller of auxiliary mode settings. The client must return all auxiliary elements, including those that have been disabled or are undefined, by sending this message for all auxiliary slots.

Command	Msg Id	Direction	Data	Type	Notes
MSP_SET_MODE_RANGE	35	to FC	sequence id	uint8	A monotonically increasing ID, from 0 to the number of slots -1
			permanentId	uint8	See Modes.md for a definition of the permanent ids
			auxChannelIndex	uint8	The Aux switch number (indexed from 0)
			rangeStartStep	uint8	The start value for this element in 'blocks' of 25 where 0 == 900 and 48 == 2100
			rangeEndStep	uint8	The end value for this element in 'blocks' of 25 where 0 == 900 and 48 == 2100

Implementation Notes

The client should make no assumptions about the number of slots available. Rather, the number should be computed from the size of the MSP_MODE_RANGES message divided by the size of the returned data element (4 bytes);
The client should ensure that all changed items are returned to the flight controller, including those where a switch or range has been disabled;
A 'null' return (with rangeStartStep == rangeEndStep) must be made for all unused slots, up to the maximum number of slots calculated from the initial message.

Deprecated MSP

The following MSP commands are replaced by the MSP_MODE_RANGES and MSP_SET_MODE_RANGE extensions, and are not recognised by cleanflight where CAP_CLEANFLIGHT_CONFIG is set.

MSP_BOX
MSP_SET_BOX

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