Hi Ramesh, On Wednesday 02 December 2009 05:37:23 Ramesh Rajagopal wrote: > Hi Laurent, > During enumeration the device is sending the proper dwMaxpayloadTransferSize > to the host. In the host side also, it is refelecting. But when we start > streaming, the host application is doing SET_CUR call of PROBE which is > sending "0" to the device and device is sending back the same value to host. > In case of ISOC also this value is being reset to "0" where as ISOC consider > dwMaxFrameSize which it got from the host application and sending the same > to the device. Due to this, ISOC doesn't fail.
According to the UVC 1.1 specification, table 4-47, the dwMaxPayloadTransferSize field "is set by the device and read only from the host". Your device must ignore the value sent by the host, and send back the right value when queried with GET_CUR. > This is what happens, Please explain is there anything I am missing. When > we start the streaming on the host side this uvc_v4l2_try_format gets called > under VIDIOC_S_FMT cmd. Here variable "probe" is being memset and assigned > a few values. This "probe" is value is sent to the device with "SET_CUR" > request. Device is copying these variable and the followed by GET_CUR > request is getting back the same value of "SET_CUR". Because of this, > dwMaxPayloadSize is being reset to "0". > > If it is a device side bug means, the SET_CUR value should not be copied > inside the device thats what you are telling. That's correct. According to the UVC specification, the device should not copy the dwMaxPayloadTransferSize value sent by the host. > But in case of ISOC alos I do copy and send back the same value during the > call of GET_CUR. Please explain where am I missing. In the isochronous case it works because the driver uses the dwMaxPayloadTransferSize to select the alternate setting, and has a workaround for devices that return a 0 value. -- Regards, Laurent Pinchart _______________________________________________ Linux-uvc-devel mailing list Linux-uvc-devel@lists.berlios.de https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
