mirror of https://github.com/ArduPilot/ardupilot
33 lines
2.1 KiB
Markdown
33 lines
2.1 KiB
Markdown
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The JSON SITL backend allows software to easily interface with ArduPilot using a standard JSON interface.
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To launch the JSON backend run SITL with ```-f json:127.0.0.1``` where 127.0.0.1 is replaced with the IP the physics backend is running at.
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Connection to SITL is made via a UDP link, port 9002 should be used to receive inputs from ArduPilot and port 9003 to return attitude information to ArduPilot.
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SITL output
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Data is output from SITL in a binary format:
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```
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uint32_t frame_count
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float Speedup
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uint16_t pwm[16]
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```
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The frame_count will increment for each output frame sent by ArduPilot, this count can be used to detect lost or duplicate frames. This count will be reset when SITL is re-started allowing the physics backend to reset the vehicle. If not input data is received after 10 seconds ArduPilot will re-send the output frame without incrementing the counter. This allows the physics model to be restarted and re-connect. Note that this may fill up the input buffer of the physics backend after some time. Speed up is the desired speed up as set with the SIM_SPEEDUP param, this is a target only. PWM is a array of 16 servo values in micro seconds, typically in the 1000 to 2000 range as set by the servo output functions.
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SITL input
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Data is received from the physics backend in a plain text JSON format. The data must contain the following fields:
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```
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timestamp (us) physics time
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imu:
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gyro(roll, pitch, yaw) (radians/sec) body frame
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accel_body(north, east, down) (m/s^2) body frame
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position(north, east, down) (m) earth frame
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attitude(roll, pitch yaw) (radians)
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velocity(north, east,down) (m/s) earth frame
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```
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This is a example input frame, it should be preceded by and terminated with a carriage return ("\n") :
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```
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{"timestamp":2500,"imu":{"gyro":[0,0,0],"accel_body":[0,0,0]},"position":[0,0,0],"attitude":[0,0,0],"velocity":[0,0,0]}
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```
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The order of fields is not important, this is minimum required fields. In the future a support for a number of additional optional felids will be added to allow readings to be provided for sensors such as airspeed and lidar.
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