Jetson Serial Communication - Autonomous-Motorsports-Purdue/Electrical_Documentation GitHub Wiki
Overview
The MCU and Jetson are connected via a USB serial connection which is used to send packets of data back and forth between the two devices. The Jetson is responsible for calculating the values to be sent to the motor, steering, brake, etc. This control data is contained in this packet and each byte of the packet is a specific instruction to the MCU. The structure of the packet is laid out below.
Packet Structure
| Packet Structure | Binary | Hex | Decimal |
|---|---|---|---|
| Start byte | 00000010 | 02 | 2 |
| Kart mode | 11110000, 11110001, 11110010 | f0, f1, f2 | 241,242,243 |
| Data length | 11100011 | e3 | 227 |
| Brake control | 00000000-11111111 | 00-ff | 0-255 |
| Throttle control | 00000000-11111111 | 00-ff | 0-255 |
| Steering control | 00000000-11111111 | 00-ff | 0-255 |
| CRC | 00000000-11111111 | 00-ff | 0-255 |
| Stop byte | 00000011 | 03 | 3 |
Control Details
The start byte will always be 2
The kart mode enumerates from f0 - f2 which sets the kart to enable, drive and kill states respectively.
The data length packet can be e1, e2, or e3 which will determine how much data is being sent to the kart.
- e1, only throttle control
- e2, throttle and steering
- e3, brake, throttle, and steering
Brake, throttle, and steering control all vary between 0 and 255 for full-on and full-off values. (for steering 0 is left and 255 is right)
The cyclical redundancy check (CRC) is a sum of all of the previous bytes that have been sent, if the number overflows wrap around 255 (sum = (sum + byte) % 255)
The Stop byte will always be 3
Example Packets
| Packet Structure | Binary | Hex | Decimal |
|---|---|---|---|
| Start byte | 00000010 | 02 | 2 |
| Kart mode (control) | 11110001 | f1 | 242 |
| Data length (3) | 11100011 | e3 | 227 |
| Brake control (set 0) | 00000000 | 00 | 0 |
| Throttle control (set 0) | 00000000 | 00 | 0 |
| Steering control (set center) | 01111111 | 7f | 127 |
| CRC | 01010101 | 55 | 85 |
| Stop byte | 00000011 | 03 | 3 |
| Packet Structure | Binary | Hex | Decimal |
|---|---|---|---|
| Start byte | 00000010 | 02 | 2 |
| Kart mode (control) | 11110001 | f1 | 242 |
| Data length (2) | 11100010 | e2 | 226 |
| Throttle control (set max) | 11111111 | ff | 255 |
| Steering control (set right) | 11111111 | ff | 255 |
| CRC | 11010011 | d3 | 211 |
| Stop byte | 00000011 | 03 | 3 |