On Fri, 19 Mar 2004, Brad Campbell wrote:
> Funny you should mention that, It's exactly what I spent all morning doing
>
> After more investigation it comes down to 4 bytes that cross the sector boundary
>
> bklaptop:~>hexdump lf3
> 0000000 0000 0000 0000 0000 0000 0000 0000 0000
> *
> 00001f0 0000 0000 0000 0000 0000 0000 0000 ffff
> 0000200 ffff
> 0000202
>
> I now have a file that is 514 bytes, it's all zero's until the last 4 bytes.
> It started with ffbb ffff in that file I posted lastnight, but I have reproduced it
> with the file
> hexdumped above.
That suggests a few questions -- you're probably already way ahead of me.
Does it matter what's in the first 510 bytes (or the 510 that
follow, since I/O always goes in multiples of 512 bytes)?
Does it have to be four 0xff's? You said 0xbb in one of the
positions would also cause a problem.
> Syslog is the same as the last one I posted.
>
> I wrote a quick and dirty bash script that transfered the entire avi
> file 512 bytes at a time using multiple calls to dd and had no problems
> copying the enitre 16mb file onto the drive, but send a packet that has
> something like the above sequence crossing a sector boundary and it will
> latch up every time.
The difference may be the sequence of bits going across the wire. Certain
bit patterns may cause problems for the packet-reassembly circuitry in the
Genesys interface.
Does it matter which sector boundary, that is, where on the drive the file
gets written?
> I'm going to try an knock up a script to narrow down the combination of
> bytes, but it's slow going as every time it latches up I have to unplug
> it, rmmod usb-storage, power cycle the drive and wait for it to do it's
> power on seek and then re-plug the drive. I'm just waiting for the
> repeated rapid power cycles to kill the disk now.
Do you have a Windows system you can use to write a file containing the
bad byte sequence? It you do, does it work? If it does, how can we find
out what's different? Maybe Windows deliberately breaks up the
transmission when it sees the forbidden sequence crossing a sector
boundary.
Alan Stern
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