[ removed Cc stable for the rest of the discussion ] On Tue, Aug 24, 2021 at 03:25:16PM +0200, Johan Hovold wrote: > Zero-length packets are used to indicate completion of bulk transfers > that are multiples of the endpoint max-packet size (as per the USB > spec). Without those the host controller driver doesn't now that the > transfer is complete and that it should call the driver completion > callback (and instead waits for the other completion conditions). Thanks for the explanation. I guess that in my case, given that the serial port would emit lots of continuous data (e.g. "find /" or "dmesg"), there's always something pending and the risk that it ends exactly on a 64-byte boundary remained low and never happened in practice. > It may be possible to configure the device to send ZLPs somehow but > since there's no public documentation for the protocol that may require > some reverse engineering. I totally understand. I'll drop my CH34x adapters and try to figure more suitable ones (i.e. some which work *by default* under Linux). Their small footprint was nice but without doc they're only usable for low speeds :-/ Thanks! Willy
