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CSW                                                            DEBUG subcommand

Use the CSW subcommand to display at the terminal the contents of the CSW
(channel status word) as it existed at the time the debug environment was
entered.

The format of the CSW subcommand is:
+----------+------------------------------------------------------------------+
| CSW      |                                                                  |
+----------+------------------------------------------------------------------+


Usage Notes:

1.  The CSW indicates the status of the channel or an input/output device, or
    the conditions under which an I/O operation terminated.  The CSW is formed
    in the channel and stored in storage location X'40' when an I/O
    interruption occurs.  If I/O interruptions are suppressed, the CSW is
    stored when the next Start I/O, Test I/O, or Halt I/O instruction is
    executed.

2.  Whenever an I/O operation abnormally terminates, issue the CSW subcommand.
    The status and residual count information in the CSW is very useful in
    debugging.  Also, use the CSW to calculate the address of the last executed
    CCW (subtract eight bytes from the command address to find the address of
    the last CCW executed).

Responses:

The contents of the CSW are displayed at the terminal in hexadecimal
representation.  Its format is:

Bits     Contents

0-3      The protection key is moved to the CSW from the CAW.  It shows the
         protection key at the time the I/O operation started.  The contents of
         this field are not affected by programming errors detected by the
         channel or by the condition causing termination of the operation.

4-7      This field is not used and must contain binary zeros.

8-31     The command address contains a storage address (in hexadecimal
         representation) that is eight bytes greater than the address of the
         last CCW executed.

32-47    The status bits indicate the conditions in the device or channel that
         caused the CSW to be stored.

48-63    The residual count is the difference between the number of bytes
         specified in the last executed CCW and the number of bytes that were
         actually transferred.  When an input operation is terminated, the
         difference between the original count in the CCW and the residual
         count in the CSW is equal to the number of bytes transferred to
         storage; on an output operation, the difference is equal to the number
         of bytes transferred to the I/O device.