[pybricksdev] Currently intended way to send data to hub?

[Novakasa]

Hi all,

Currently, I am unsure what the intended way to send data to the hub in pybricksdev using PybricksHub, on the latest commit and most recent firmware obtained from Pybricks Code.
There is the method PybricksHub.send_block that is used to download the program, but trying to use that method myself results in checksum errors:

import asyncio
from pybricksdev.connections import PybricksHub
from pybricksdev.ble import find_device

async def main():
    hub = PybricksHub()
    device = await find_device("Pybricks Hub")
    await hub.connect(device)
    await hub.run("auto_train_updated.py", wait=False)
    while not hub.program_running:
        await asyncio.sleep(0.5)
    await hub.send_block(b"message")
    await hub.user_program_stopped.wait()

asyncio.run(main())

Output (line 6 is proper output from my program):

[...]
Progress: 92%
Progress: 95%
Progress: 98%
Progress: 100%
data::{'key': 'state_changed', 'data': 'stopped'}$
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\nm\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\nm\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\ne\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\ne\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\ns\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\ns\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\ns\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\ns\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\na\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\na\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\ng\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\ng\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103
Exception in callback PybricksHub.nus_handler(21, bytearray(b'g...age\r\ne\r\n'))
handle: <Handle PybricksHub.nus_handler(21, bytearray(b'g...age\r\ne\r\n'))>
Traceback (most recent call last):
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\asyncio\events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\lolli\miniconda3\envs\brickrail\lib\site-packages\pybricksdev\connections.py", line 623, in nus_handler
    raise RuntimeError(
RuntimeError: Expected checksum 107 but got 103

Curiously, if I send longer data, the last few characters of my message is properly received. This is independent of how long after starting the program I wait to send the data.
For the message: "cmd::train.start()", typically only ".start()" is received, but in one case I was only missing the first character, and in one case I received "n.start()".

When running the same script via Pybricks Code and mashing on the keyboard, the program properly responds to the sent data:

got message
1
got message
2
got message
3
got message
4
got message
z
got message

[dlech]

send_block is for sending the program and not for general use. Try this instead:

from pybricksdev.connections import NUS_RX_UUID

...

    await hub.client.write_gatt_char(NUS_RX_UUID, b"message", False)

[Novakasa]

Alright, that works, thanks!

[dlech]

FYI, max payload is 20 bytes for this method.