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发表于 2013-2-15 13:05:01
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MultiWii Serial Protocol
updated 04 July
Multiwii serial protocol was redesigned:
• to be light, as before
• to be generic: it can be used transparenlty by a GUI, OSD, telemetry or home made config tool.
ie no more specific OSD code should be coded in multiwii
• to be bit wire efficient: only requested data are transmitted in a binary format
• to be quite secure: data are sent with a checksum, preventing corrupted configuration to be injected.
• to be header sensitive: as it is designed with a specific header, it can be mixed with other frame, like GPS frame
ie, it will be possible to connect either a GUI or a GPS on the same serial port without changing the conf
• to be less sensitive to evolutions:
ie in case of parameter evolution, the main protocol will remain compatible and the GUI will be much less version dependent.
variable data length allows to consider only the beginning of a message, leaving the other octets at the end to extend transparently the message (for instance to add a new PID)
I thought first about an implementation of Mavlink, but I think it's not what I was looking for.
Even with a partial implementation, the predefined structures are not light enough for what I have in mind.
Some messages are however inspired from mavlink structure.
The main rule remains: Multiwii never sends something on its own.
A request must be done in each case to retrieve or set data.
Each messages received are acknowledged even if there is no data inside.
There are 2 main messages to consider:
•request message to multiwii
•multiwii output message
request message to multiwii
To request simple data without parameters / send a specific command / inject new parameters in multiwii
messages are formated like this:
$M>[data length][code][data][checksum]
1 octet '$'
1 octet 'M'
1 octet '<'
1 octet [data length]
1 octet [code]
several octets [data]
1 octet [checksum]
[data length] can be 0 in case of no param command
multiwii output message
messages are formated like this:
$M>[data length][code][data][checksum]
1 octet '$'
1 octet 'M'
1 octet '>'
1 octet [data length]
1 octet [code]
several octets [data]
1 octet [checksum]
if the message is unknown:
$M|[0][code][checksum]
1 octet '$'
1 octet 'M'
1 octet '|'
1 octet 0
1 octet [unknown code]
1 octet [checksum]
list of message codes
multiwii output message
MSP_IDENT
multitype + version
MSP_STATUS
cycletime & errors_count & sensor present & box activation
MSP_RAW_IMU
9 DOF output
MSP_SERVO
8 servos
MSP_MOTOR
8 motors
MSP_RC
8 rc chan
MSP_RAW_GPS
fix, numsat, lat, lon, alt, speed
MSP_COMP_GPS
distance to home, direction to home
MSP_ATTITUDE
angles and heading
MSP_ALTITUDE
altitude
MSP_BAT
vbat, powermetersum
MSP_RC_TUNING
rc rate, rc expo, rollpitch rate, yaw rate, dyn throttle PID
MSP_PID
table of P I D
MSP_BOX
tabl of checkbox
MSP_MISC
powermeter trig
MSP_MOTOR_PINS
which pins are in use for motors & servos, for GUI
MSP_BOXNAMES
the textual aux switch names (it's a way to build a more generic GUI, allowing an easier extension for future checkbox)
MSP_PIDNAMES
the textual PID names
MSP_WP
get a WP, WP# is in the payload, returns (WP#, lat, lon, alt, flags) WP#0-home, WP#16-poshold
MSP_DEBUG
debug1,debug2,debug3,debug4 variable
multiwii input message
MSP_SET_RAW_RC
8 rc chan: it's a way to command multiwii via a "serial RC transmitter"
MSP_SET_RAW_GPS
fix, numsat, lat, lon, alt, speed: it's a way to inject in multiwii GPS data coming for instance from an OSD with an integrated GPS
MSP_SET_PID
8 P I D
MSP_SET_BOX
11 checkbox
MSP_SET_RC_TUNING
rc rate, rc expo, rollpitch rate, yaw rate, dyn throttle PID
MSP_ACC_CALIBRATION
to calibrate ACC
MSP_MAG_CALIBRATION
to calibrate MAG
MSP_SET_MISC
powermeter trig
MSP_RESET_CONF
to reset all params to default (new feature)
MSP_EEPROM_WRITE
to write current params to EEPROM |
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