Wit-Motion GPS/IMU Device Parser

Introduction

I needed a IMU and a GNSS/GPS device for a project, and I fould this one on Amazon:

Compile

gcc main.c -o main

Run

./main
ACC  : 0.059570, -0.009277, 1.001465
TEMP : 33.360001
GYRO : 0.000000, 0.000000, 0.000000
ANGLE: -0.532837, -3.619995, 81.128540
VERS : 18155
MAG  : 2073, 396, -5017
PRESS: 1005.570007
ALT  : 428939665
LONG : 33.621915
LAT  : 34.919429
GPS H: 32.000000
GPS Y: 340.489990
GPS S: 0.000000
GPS N: 15
POS A: 1.100000
POS H: 0.700000
POS V: 0.900000
QUART: 0.759338, 0.016998, 1.972992, 0.649841

NOTE: Use CTRL-C to exit the application

Wit Motion Standard Protocol

The device home page is here: [https://www.wit-motion.com/InertialNavigationSensor/35.html]

NOTE: The code samples are pretty awful. YMMV.

There is a protocol description document here: [https://wit-motion.gitbook.io/witmotion-sdk/wit-standard-protocol/wit-standard-communication-protocol]

NOTE: The protocol description document is not great, it doesn't give units and conversions properly, and I still have no idea what data the Altimeter is giving me or how to decode it.

Debugging

Okay, so after debugging, it seems that we need to read one byte at a time, the device cannot handle multibyte read from the buffer, after building a readloop that begins from 0x55, we have the following:

BUF: 0x55 0x51 0x32 0x00 0x69 0x00 0x01 0x08 0x10 0x0c 0x66
BUF: 0x55 0x52 0x00 0x00 0x00 0x00 0x00 0x00 0x10 0x0c 0xc3
BUF: 0x55 0x53 0x1f 0x02 0x02 0xff 0xd6 0x05 0xeb 0x46 0xd6
BUF: 0x55 0x54 0xcb 0x00 0x61 0x0a 0x31 0xee 0x00 0x00 0xfe
BUF: 0x55 0x56 0x6b 0x8a 0x01 0x00 0xc8 0x0b 0x00 0x00 0x74
BUF: 0x55 0x57 0xc2 0x57 0xe4 0x13 0x63 0x2a 0x98 0x14 0xf5
BUF: 0x55 0x58 0x18 0x01 0xae 0x2e 0x00 0x00 0x00 0x00 0xa2
BUF: 0x55 0x59 0x9c 0x7f 0x6f 0x03 0xaf 0xfe 0x32 0x09 0x23
BUF: 0x55 0x5a 0x11 0x00 0x82 0x00 0x50 0x00 0x64 0x00 0xf6
BUF: 0x55 0x51 0x32 0x00 0x6a 0x00 0x00 0x08 0x10 0x0c 0x66
BUF: 0x55 0x52 0x00 0x00 0x00 0x00 0x00 0x00 0x10 0x0c 0xc3
BUF: 0x55 0x53 0x1e 0x02 0x02 0xff 0xd6 0x05 0xeb 0x46 0xd5
BUF: 0x55 0x54 0xca 0x00 0x7b 0x0a 0x29 0xee 0x00 0x00 0x0f
BUF: 0x55 0x56 0x6b 0x8a 0x01 0x00 0xc8 0x0b 0x00 0x00 0x74
BUF: 0x55 0x57 0xc2 0x57 0xe4 0x13 0x64 0x2a 0x98 0x14 0xf6
BUF: 0x55 0x58 0x18 0x01 0xae 0x2e 0x00 0x00 0x00 0x00 0xa2
BUF: 0x55 0x59 0x9c 0x7f 0x6f 0x03 0xaf 0xfe 0x32 0x09 0x23
BUF: 0x55 0x5a 0x11 0x00 0x82 0x00 0x50 0x00 0x64 0x00 0xf6
BUF: 0x55 0x51 0x32 0x00 0x6c 0x00 0x01 0x08 0x11 0x0c 0x6a
BUF: 0x55 0x52 0x00 0x00 0x00 0x00 0x00 0x00 0x11 0x0c 0xc4
BUF: 0x55 0x53 0x1e 0x02 0x02 0xff 0xd6 0x05 0xeb 0x46 0xd5
BUF: 0x55 0x54 0xd0 0x00 0x74 0x0a 0x2d 0xee 0x00 0x00 0x12
BUF: 0x55 0x56 0x6b 0x8a 0x01 0x00 0xc8 0x0b 0x00 0x00 0x74
BUF: 0x55 0x57 0xc2 0x57 0xe4 0x13 0x64 0x2a 0x98 0x14 0xf6
BUF: 0x55 0x58 0x18 0x01 0xae 0x2e 0x00 0x00 0x00 0x00 0xa2
BUF: 0x55 0x59 0x9c 0x7f 0x6e 0x03 0xaf 0xfe 0x32 0x09 0x22
BUF: 0x55 0x5a 0x11 0x00 0x82 0x00 0x50 0x00 0x64 0x00 0xf6
BUF: 0x55 0x51 0x2f 0x00 0x6b 0x00 0x00 0x08 0x0d 0x0c 0x61
BUF: 0x55 0x52 0x00 0x00 0x00 0x00 0x00 0x00 0x0d 0x0c 0xc0
BUF: 0x55 0x53 0x1e 0x02 0x02 0xff 0xd6 0x05 0xeb 0x46 0xd5
BUF: 0x55 0x54 0xe4 0x00 0x7b 0x0a 0x2c 0xee 0x00 0x00 0x2c
BUF: 0x55 0x56 0x6b 0x8a 0x01 0x00 0xc8 0x0b 0x00 0x00 0x74

NOTE: we need the CRC in place to throw data that does not have the full 11 bytes because there may be a 0x55 in the byte buffer that kills the read loop.