a ZLP has to be send when the length of payload data is exactly an integer multiple of wMaxPacketSize The USB spec defines that if the last packet of a bulk transfer has the exact size of the endpoint max packet size, the whole transfer must be terminated by a zero length urb.

So in the case of a transfer which is an integer multiple of max-packet-length, a ZLP is used for demarcation. You see this in bulk pipes a lot. For example, if you have a 4096 byte transfer, that will be broken down into an integer number of max-length packets plus one zero-length-packet.

May 23, 2012 · Is there a way to send ZPL (Zebra Programming Language) to a printer in .NET? I have the code to do this in Delphi, but it is not pretty and I would rather not try to recreate it in .NET as it is.

Feb 25, 2018 · No its not transparent. Your code needs to deal with ZLP (Zero Length packet). If you do not deal with ZLP, you may see wrong behaviors. Usually Short packets are sent as the last packet automatically because the length was not aligned to the max packet size boundary. But ZLP needs a extra transfer request from user space. –

Oct 6, 2024 · In such code, you should send a ZLP if the previous packet was equal to the maximum packet size and you cannot submit the next packet immediately (as no further data is ready for transmission). On a full-blown operating system, the operating system usually takes care of this and doesn't give you control over individual USB packets.

Apr 11, 2017 · In VB I would do a filecopy command from a temp text file with the raw ZLP in it and copy that textfile to that port. (in other words I save the ZPL string to a file and then copy that file to the serial port). I'm sure Java can do something similar.

Aug 10, 2016 · Hi again CJC, I'm sorry if the explanation isn't clear, as the thought of a zero-byte transfer seems like something I'd never have to think about nor breakdown.

Sep 23, 2019 · I'm using ZebraDesigner 2.2.2 (Build 2728). Is there a way to extract the ZPL code from ZebraDesigner? I can't even export it to ZPL file, the only option I have is saving it as .lbl.

May 16, 2010 · In the context of a DFU driver, I'm trying to respond with a packet of length zero (not ZLP as in multiples of max size, just zero bytes) to a USB control in transfer. However, the host returns with a timeout condition.

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