> From: Anton Tikhomirov [mailto:av.tikhomirov@xxxxxxxxxxx] > Sent: Wednesday, December 18, 2013 11:18 PM > > > > On Thu, Dec 19, 2013 at 11:32:08AM +0900, Anton Tikhomirov wrote: > > > > Hi, > > > > > > > > > Hi, > > > > > > > > > > On Tue, Dec 17, 2013 at 03:59:31PM +0900, Anton Tikhomirov wrote: > > > > > > In accordance with specification, when sent data length is > > > > > > > > > > please mention section of specification. > > > > > > > > USB2.0 spec., 8.5.3.2 Variable-length Data Stage > > > > > > > > > > > > > > > an exact multiple of wMaxPacketSize for the pipe and less > > > > > > than requested by host, the function shall return a zero-length > > > > > > packet (ZLP) to indicate the end of the Data stage to a USB host. > > > > > > > > > > hmm... so in USB3 mode that would be host requesting 513 bytes and us > > > > > sending only 512. > > > > > > > > Our customer reported this issue. In their case, Windows USB2.0 host > > > > requests Configuration descriptor with wLength = 255. Device replies > > > > with two 64 bytes IN transactions, and stalls EP0 on 3rd IN transaction, > > > > where it has to reply with ZLP. Unfortunately, we don’t have full > > > > picture of what's happening on their side and why host requests > > > > more bytes than actual length of Configuration descriptor. > > > > > > that's a bug on the host side. > > > > Certainly not. The host doesn't know how big the Configuration descriptor > > is, so it always asks for 255 bytes (on Windows that is, I'm not sure > > about Linux). > > As far as I know, first time Windows host requests only 9 bytes of > Configuration descriptor, which include total size of Configuration > descriptor and its subordinates. Then, second time it requests > Configuration descriptor again and uses total length obtained in first > step. Am I wrong? I think it does that for the Device descriptor, but not the Configuration descriptor, for some reason. It could depend on which version of Windows you have, too. My point was that it is not a bug for the host to ask for more bytes than the length of the descriptor, just as it is not a bug to ask for fewer bytes than the length of the descriptor. The device must handle both cases. -- Paul ��.n��������+%������w��{.n�����{���)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
