On Thu, 4 Jan 2007, Oliver Neukum wrote: > Hi, > > quoting from the WCM spec: > - > The firmware shall interpret GET_ENCAPSULATED_RESPONSE as a request to read > response bytes. The firmware shall send the next wLength bytes from the > response. The firmware shall allow the host to retrieve data using any > number of GET_ENCAPSULATED_RESPONSES. The firmware shall return a zero-length > reply if there are no data bytes available. > The firmware shall send RESPONSE_AVAILABLE notifications periodically, using > any appropriate algorithm, to inform the host that there is data available > in the reply buffer. The firmware is allowed to send RESPONSE_AVAILABLE > notifications even if there is no data available, but this will obviously > reduce overall performance. > - > > Do I read this correctly to mean that I must not treat zero bytes from > GET_ENCAPSULATED_RESPONSE as an error, because RESPONSE_AVAILABLE > is reliable in one direction only?
The spec certainly says that 0 bytes from GET_ENCAPSULATED_RESPONSE is not an error. I don't know what you mean by "RESPONSE_AVAILABLE is reliable in one direction only". The message should be treated as a hint that data may be available so the host should attempt to start a transfer -- but it's still possible that no data bytes are available. Alan Stern ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
