RE: [libdc1394-devel] interpretation of format 7 [was: format7 dm a functions...]
Capture and control API for IIDC compliant cameras
Brought to you by:
ddouxchamps,
gordp
From: Michael S. <sch...@im...> - 2002-11-19 16:57:53
|
On 19 Nov 2002 at 17:45, Gramatke, M. wrote: > Hello Damien, > > > From: Damien Douxchamps [mailto:d.d...@te...] > > Sent: Tuesday, November 19, 2002 5:57 PM > > > if a 1.20 camera does not use padding, and thus outputs the > > beginning of > > the next frame in the last packet from the previous frame. Do the 1394 > > specs allow this kind of strange behavior? > > That's nice to gain the last drachm of bandwidth. But as far as I know, a > DMA controller relies on the so called sy bit in the header of a packet. > This bit is set to mark the very first packet of an image and tells the > controller to update its destination address. Thus such a crossover packet > must be marked. But the data crossover is somewhere inside the data block of > this package and worse, this point moves image by image. I doubt that any > DMA controller on earth can handle that. > > So if you want to do that, you have to abandon the sy bit and let the DMA > write continuously write into memory. Maybe this the intention of what is > the so called Multi_Shot in the IIDC. > > Martin > Hello, The IIDC V1.30 says in Section 1.9.7: If BytePerPacket * n != BytePerFrame (n is integer), you must use padding. That means as Martin Gramatke pointed out, that the first byte of one frame must be the first byte of one packet (the one with the sy bits set in the isoch. header). Adding the beginning of one frame to the end of the previous frame in one packet is not allowed by IIDC. Hope this answers the question. Best regards, Michael Scholles -- +---+---+-+-+-+-+ +---------------------------------------+ | | |_|_|_|_| | Michael Scholles | |___|___|_|_|_|_| | Fraunhofer-Institute of | | | |_|_|_|_| | Microelectronic Circuits and Systems | |___|___|_|_|_|_| | Grenzstrasse 28; 01109 Dresden/Germany| | __ __ | | Phone: +49-(0)351-8823-201 | | /_ /_ /_ | | Fax: +49-(0)351-8823-266 | |/ / / /_/ | | email: mic...@im... | | | | URL: http://www.ims.fhg.de | +-------+-------+ +---------------------------------------+ |