RE: [libdc1394-devel] interpretation of format 7 [was: format7 dm a functions...]

[Gramatke, M. <Mar...@ba...>]

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