[sane-devel] "a second try" the thread I had had started a while ago

Dieter Jurzitza dieter.jurzitza at t-online.de
Sat Aug 13 05:04:59 UTC 2005

Dear listmembers,
to come back to the issue I found (and thanks to Henning somewhat solved). My 
situation: a scanner and a zipdrive (SCSI) sitting on the same SCSI bus on 
ID5 (zipdrive) and ID6 (scanner / MUSTEK 12000SP).

Problem description:
if the light of the scanner is off (after several minutes of inactivity) and a 
scan is started, there is always a SCSI-timeout of the zipdrive that leads to 
system crashes every other time.

By the way: the zipdrive is at the end of the cable & is actively termiated, 
the controller is an AHA 2940U and the termination is set to automatic. Both 
devices work flawlessly in case the scanner is awake (i.e. it's lamp is on) 
and therefore reacts fast to requests.
I have been using this exact configuration for years with the old kernel 2.4.X 

Assumed cause:(?)
I think the hotplug - system checks for the status of the SCSI-bus devices 
every other time. When the scanner is asked for data and has been off, it 
allocates the bus (old fashioned) and does not release it until it is ready 
for scanning. Therefore the other device on the same bus seems to timeout
because a request to it is not serviced as long as the scanner blocks the bus.
With kernel 2.4 there were no periodic requests if the zipdrive (in my case) 
was not in use.

Is there any other solution for this than removing the device (zipdrive) by 

echo "scsi remove-single-device 1 0 5 0" > /proc/scsi/scsi

and reactivating it for actual usage? I would have wanted to increase the 
timeout value up to 40s or something similar. But maybe this is not how it 
should be .....

Many thanks for any efforts in advance,
take care

Dieter Jurzitza


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