Re: [libdc1394-devel] memory problems

[Jon S. <jon...@ho...>]

On Thu, 2007-02-01 at 09:12 -0500, Daniel Drake wrote:
> On Wed, 2007-01-31 at 13:51 -0600, Jon Schewe wrote:
> > Ok, I did some more looking into this and it really looks like asking
> > for more than one register at a time is probably not going to do what
> > you want, GetCameraControlRegisters.  The num_regs value that is passed
> > in is sent directly to the raw1394 driver in the linux kernel as the
> > length of the data requested.  If this length is equal to 4, then a quad
> > read is done, otherwise a block read is done.  This is probably why 4
> > times the actual length is passed into various functions in many places
> > as the quad read is probably what you want in most places.  So I'd
> > suggest removing the ability to read multiple registers at once and read
> > them one at a time.  I don't see this functionality being used much
> > inside the library, can we just remove it?
> 
> It's used extensively for uploading shading images to AVT cameras.
> Removing it and doing it reg-by-reg would make this reaaaaalllly
> sllooooow :)
> 
> I haven't been keeping up with the discussions, but the patch I wrote to
> enable reading of multiple registers didn't change any behaviour for the
> single register read case. I'm not sure which problems you are trying to
> solve but I doubt that removing this functionality would fix anything.
> 
> Here's the original patch:
> http://www.reactivated.net/patches/libdc1394/2.0.0-rc3/multi-reg-access.patch

Does reading of multiple registers actually work?  I've been through the
kernel source and I don't see how it could as the kernel is checking for
a length of exactly 4 to decide which type of read to use.  So if you
specify you want to read 1 register, the length is 4 and a quad read is
used.  If you specify anything else, then length will not be 4 and a
block read will be used.


________________________________________________________________________
http://lug.htc.honeywell.com/people/jschewe [Honeywell Intranet Only]
*My views may not represent those of my employers