Re: Random SCSI lockup during start NetBSD 6.0

[Ignatios Souvatzis <is%netbsd.org@localhost>]

Hi Dennis,

On Sat, Dec 15, 2012 at 03:10:52AM +0000, Dennis Boon wrote:
> 
> Sorry to bother you guys again, this time maybe with something not related to 
> NetBSD:
> 
> During the startup of NetBSD on my A3000 I get a random lockup on the SCSI 
> bus 
> right after the following (I left out the bits between the <> brackets:
> 
> ahsc0: target now synchronous, period=224ns, offset=12
> sd0 at scsibus0 target 0 lun 0: <my HD description>
> sd0: <drive geometry>
> 
> Then it hangs sometimes, with the HD light staying on. At the
> moment, the HD is
> the only SCSI device on the chain. The HD is connected through a 68 pins 
> connector on the HD to the 68 pins cable to the 68 to 50 pins adapter to the 
> 50 
> pins connector on the mainboard on one side. The other side on the cable is 
> actively terminated with a 68 pins terminator.

If you do that, you have to make sure both halves of the scsi bus are
terminated twice - once at the 68 to 50 pin connector. 

If it's a simple connector, it might be intended to connect 50 pin
devices in the middle of an 68pin bus.

Easiest is, you would need two 68pin terminators at both ends of
the bus, and connect your 50 pin HBA through the 50-68 pin connector
*without intermediate cable!!!* to the 68pin cable.  (and not
terminate on the mainboard!).

ONLY IF your connector does terminate the upper half of the bus, you can
connect it to one end of the 68pin cable, to prolong it as a 50pin cable.

You should also avoid having any prolonged Y-configurations. or parts 
of the bus with three terminators.

And for completeness: any 68-50-68 configuration will damage data if the
computer is not in the 50 part - as two 68-capable devices will detect
each other and talk in wide to each other, only transfering every other
byte.

If you violate these conditions, your bus is not properly terminated and
yes, an *occasional* hang during synchronous mode is expected.


Regards,
        -is


ASCII GRAPHICS:

T___ 68pin terminator
T

T    50pin terminator

#    simple connector


T    68-50-connector terminating the upper half of the wide bus.
#

working::

T=======#==================T
T=======#==============#===T
        "              |
      68pindev.      50pin

working::

T=======#==============T
T=======#==============#==50pindevice=T
        "              
    68pindev.


not working:
T=======#==============#
T=======#==============#==50pindevice-T
        "              
    68pindev.