[libdc1394-devel] How exactly the DMA works witha webcam that use libdc1394

[Erio G. <gri...@ti...>]

Hello to all of the m-list,
we use a firewire camera on a real-time robot application; we try to use all
of the frame that the camera can give us but studing the DMA, something is
understable to us:

How the driver can always give the newer image in a minumum time using only
one position of the ring buffer? We are used to see a buffer that return the
last complete image acquired, acquiring continually in all the buffer so not
to waste time...but
the ring buffer return only the lastbuffer position, refreshed when??

I'll try to explain better: how the driver works?
-It take a new image just after the Done_with_buffer and put that into the
lasbuffer position until the application will give another done_with_buffer?
If that's like this, if I take the image after some second i'll have an
old image!?

-It continously put the last image in the lastbuffer position until i'll
take it, and then, after the done_with_buffer the acquisition will begin
again in the following position of the ring buffer?
If that's like this sometime I have to wait the entire time of acquisition
of a frame before I can heve it!!

-or what? We can't suppose anything even if we read almos all of the source
of the lidc1394

All this doubts was born because we worked directly on the ring_buffer AFTER
the done_with_buffer...and the problem was that we work on the same image
for N time, where N is the dimension of the ring buffer...even if we always
returned the pointer to the position with the last image acquired!



Thanks for any help yiu cab give us, also link to full documentation,
Grillo&Cavicchioli of the Bicocca University of Milan,
trying to the degree