Serial through V5 controller

13056C · July 12, 2024, 8:26pm

I’ve figured out how to read from the brain, because it has the user and the comm ports but the controller only has 1.
I know it’s possible just because of the fact that the VS Code extension is able to do it but I can’t figure out how. I know I could use websockets that the vscode extension provides but I want to avoid the need for vscode for running it.

The brain is simple enough with this simple python script I can easily read the serial from the brain but when you plug it into the controller it doesn’t work.

import serial

def read_serial_data():
    try:
        ser = serial.Serial('COM17', 115200, timeout=1)
        print('Connected to VEX V5 controller.')
        
        while True:
            if ser.in_waiting > 0:
                line = ser.readline().decode('utf-8').rstrip()
                print(line)
    except serial.SerialException as e:
        print(f'Error: {e}')
    except KeyboardInterrupt:
        print('Program interrupted by user.')
    finally:
        ser.close()
        print('Serial connection closed.')

if __name__ == '__main__':
    read_serial_data()

sazrocks · July 12, 2024, 10:46pm

There’s some extra work needed. It appears that you must request bytes from the controller by sending a special command. Additionally, the controller may need to be in download mode (well, the PROS CLi sets it to download mode when doing wireless debugging). This section of code in the PROS CLI might help you get started:

github.com

purduesigbots/pros-cli/blob/c321f20a2bcbbcc442cc8ed0faed8353de6d5044/pros/serial/devices/vex/v5_device.py#L860


      
              if (version.product == V5Device.SystemVersion.Product.BRAIN and version.system_version in Spec('<1.0.13')) or \
                      (version.product == V5Device.SystemVersion.Product.CONTROLLER and version.system_version in Spec('<1.0.0-0.70')):
                  schema = '<x12B3xBI12x'
              else:
                  schema = '<x12B3xBI12xB3x'
              rx = self._txrx_ext_struct(0x22, [], schema)
              logger(__name__).debug('Completed ext 0x22 command')
              return V5Device.SystemStatus(rx)
          
          @retries
          def user_fifo_read(self) -> bytes:
              # I can't really think of a better way to only return when a full
              # COBS message was written than to just cache the data until we hit a \x00.
          
              # read/write are the same command, behavior dictated by specifying
              # length-to-read as 0xFF and providing additional payload bytes to write or
              # specifying a length-to-read and no additional data to read.
              logger(__name__).debug('Sending ext 0x27 command (read)')
              # specifying a length to read (0x40 bytes) with no additional payload data.
              tx_payload = struct.pack("<2B", self.channel_map['download'], 0x40)
              # RX length isn't always 0x40 (end of buffer reached), so don't check_length.

Tropical · July 13, 2024, 3:57pm

I’ve recently had to deal with this same problem for a CLI tool that i’ve been working on. The controller has a specialized packet for obtaining/sending user program stdio from only a V5 system port. If you aren’t working off a codebase with an existing V5 implementation for packet exchange on the system port, it might be a lot of work. Along with what charles has provided, I can point you to the _txrx_ext_packet function in pros-cli for how you can exchange extended commands.

I’m going to say that ive also had replies taken down in the past that just covered VEX tools dealing with the serial protocol, so i’m not going to go further in-depth on this forum unfortunately. My best advice is to look at the pros-cli implementation that charles linked, although from some personal testing their code misunderstands the packet structure (it does still work, though).