-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Am 04.05.2010 21:50, schrieb Mauro Carvalho Chehab: > Stefan Ringel wrote: > >>>> datagram from urb to videobuf >>>> >>>> urb copy to temp copy to 1. videobuf >>>> buffer 2. audiobuf >>>> 3. vbi >>>> 184 Packets -------> 184 * 3072 ----------> 4. etc. >>>> a 3072 bytes bytes >>>> 184 * 3072 * >>>> 3072 bytes 180 bytes >>>> (184 bytes - 4 bytes >>>> header ) >>> In order to receive 184 packets with 3072 bytes each, the USB code will >>> try to allocate the next power-of-two memory block capable of receiving >>> such data block. As: 184 * 3072 = 565248, the kernel allocator will seek >>> for a continuous block of 1 MB, that can do DMA transfers (required by >>> ehci driver). On a typical machine, due to memory fragmentation, >>> in general, there aren't many of such blocks. So, this will increase the >>> probability of not having any such large block available, causing an >> horrible >>> dump at kernel, plus a -ENOMEM on the driver, generally requiring a reboot >>> if you want to run the driver again. >>> >> And direct copy from urb to videobuf/alsa/vbi in 184 Bytes segments. >> >> urb 1. videobuf >> copy to 2. audiobuf >> 3. vbi >> 184 Packets -------> 4. etc. >> a 3072 bytes >> 180 Bytes (without headers) > > That's basically what that logic does. It preserves the header if you select > TM6000 format (so, no checks for the start of the block, etc), or copies > just the data, if you select YUY2 or UYUV. > >> or how can I copy 180 Bytes Data from 184 Bytes block with an >> anligment of 184 urb pipe (184 * 3072 Bytes)? > > A 184 x 3072 URB pipe is a big problem. We used a large pipe in the past, and this > won't work. For example, on a notebook I used to run some tests with 1 GB of > ram after starting X and do anything (like opening a browser), the URB > allocation used to fail, as there weren't any available 1MB segment at > the DMA area. Even without starting X, after a few tests, it would eventually > have fragmented the memory and the driver stops working. > > and 3072 * 46 = 141312 bytes and it can through 184 ! it's 1/4 smaller.
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