What is scsimon?

The scsimon tool allows you to capture all of the traffic on the SCSI bus and log it to a file. The data is stored in a "Value Change Data" VCD file that can be read by GTKWave

+---------+    +-----------+    +----------+
|         |    |  PiSCSI   |    | Other    |
|  HOST   |    |  running  |    | SCSI     |
|   PC    |    |  scsimon  |    | device(s)|
|         |    |           |    |          |
+-+-------+    +--+-----+--+    +------+---+
  |               |     |              |
  +---------------+     +--------------+
    SCSI Bus              SCSI Bus

Checkout and build scsimon

scsimon is included in the main installation of PiSCSI. It should be located in /usr/local/bin/scsimon. If its not, you may need to upgrade to a newer version of the PiSCSI software.

Special PiSCSI 1.5/1.6 modification

If you're using a PiSCSI 2.x board ("FULLSPEC"), you do not need this modification!

If you're using a PiSCSI version 1.5 or 1.6, you will need to make the following modification to your board. This will force all of the transceivers into a RECEIVE-ONLY mode.

Capture data

Make sure you've stopped the PiSCSI service. Then run scsimon. If you're trying to capture a specific scenario, you'll want to wait to start scsimon until immediately before the scenario.

sudo ./scsimon

Press CTRL-C when you're done capturing. You'll want to save the .VCD file.

Reviewing data

Install GTKWave and launch it

sudo apt install gtkwave
gtkwave&

Once GTKWave launches, open the .VCD file that was captured by scsimon.

First, double-click on the "logic" item in the Signal Search Tree (SST) frame.
Double-click each of the signals that show up below the SST frame. This will add them to the Wave panel.
Now, you should be able to see all of the data presented.

Note: There may be A LOT of zero data captured, since the SCSI bus may be sitting idle when you start the capture