Re: Packet writing on NEC1300
On Sun, 07 Sep 2003 00:59:23 +0200
Andy Polyakov <appro@fy.chalmers.se> wrote:
> <snip>. But as long as NEC hides behind
> "designed exclusively for Windows" and keep providing Windows software
> which applies packet writing strategy even to DVD+RW, you won't be
> able to make them address the problem "by the root" so to say.
> Unfortunately:-(
To be fair to NEC, they didn't provide me with any Windows software that
does this. They didn't provide any software at all.
> <snip>
> I/O to /dev/scdN passes through common block buffer, which is free to
> rearrange the requests. E.g. I could observe 'dd of=/dev/scdN obs=32k'
> being rearranged as a serie of 126K requests. At the beginning of
> recording that is. As recording is normally way slower than dd, block
> buffer starts starving for memory at some point and starts fragmenting
> at 2K, 4K, 14K, 31K, literally whatever chunksizes, which by the way
> can even appear in *non-ascending* order. This is confusing for your
> firmware. /dev/raw/rawM on the other hand maintains the strict order
> and fragmentation implied by the writing program. In other words 'dd
> of=/dev/raw/rawM obs=32k' results in serie of 32K requests in strictly
> asceding order. Something your firmware can bear with.
I've modified the CDRW packet writing patch
http://w1.894.telia.com/~u89404340/patches/packet/2.4/packet-2.4.21.patch.bz2
to work in combination with your patch to write to DVD+RWs. This works:
it looks like the DVD writer is happy so long as I only feed it with
32k requests. But the performance is dreadful. If I can
manage to get any sort of reasonable performance out of this, I'll send
you what I've done.
Thanks,
John
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