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Prevent FTDI Reset on Serial Open/Close (Raspberry Pi OS) #779

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Prevent FTDI Reset on Serial Open/Close (Raspberry Pi OS) #779

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e747bae
add ftdi rest fix
BioCam Dec 5, 2025
b5cbdbf
fix type checking
BioCam Dec 5, 2025
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16 changes: 16 additions & 0 deletions pylabrobot/io/serial.py
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,22 @@ def _open_serial() -> serial.Serial:
self._executor = None
raise e

assert self._ser is not None

# --- FIX: Prevent FTDI reset on open/close (critical for Inheco on Raspberry Pi) ---
Comment on lines +187 to +188
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@rickwierenga rickwierenga Dec 5, 2025

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we should avoid machine specific comments in the io layer

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@BioCam BioCam Dec 5, 2025

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I agree - but the io layer is where these commands have to be set in the right chronological order it seems?

One way we could get around this is by having an attribute for this in the io layer, default to None, i.e. leaving out this new code section, and have the backend provide the attribute if needed?

But in this scenario, I was wondering whether this is a truly unique IIS+Raspian combo or whether other machines might erroneously disconnect to the control PC too;
if others are doing the same, and this change provides no down-sides, it should be permanently added to the io I believe - just a couple of big ifs 😅

try:
# Some pyserial versions require direct attribute access:
self._ser.dtr = False
self._ser.rts = False

# Others only respect the explicit setter:
self._ser.setDTR(False)
self._ser.setRTS(False)
Comment on lines +190 to +196
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@rickwierenga rickwierenga Dec 5, 2025

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do you know which versions these are?

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@BioCam BioCam Dec 5, 2025

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Unfortunately I do not - this is all very new to me

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@rickwierenga rickwierenga Dec 5, 2025

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ok but where did you notice you have to use one or the other? is one even supported on platforms where the other isn't?


logger.info(f"[{candidate_port}] Disabled FTDI DTR/RTS (prevent USB disconnect).")
except Exception as e:
logger.warning(f"[{candidate_port}] Could not disable DTR/RTS: {e}")

self._port = candidate_port

async def stop(self):
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