DEBUG Subcommands-BREAK, CAW 6. You should set breakpoints only at valid operation code addresses;
the BREAK subcommand does not check to see whether or not the
specified location contains a valid operation code.
7 • If you reference a virtual storage you are given a nonshared
receive the message:
address that is in
copy of the segment SYSTEM sysname REPLACED WITH NON-SHARED copy a shared
and you
None.
CAW Use the CAW subcommand to display at the terminal the contents CAW (channel address word) as it existed at the time the
environment was entered. The format of the CAW subcommand is:
of the
debug r I CAW I L- -lI 1. Issue the CAW subcommand to check that the command address field
contains a valid CCW address, or to find the address of the current CCW so you can examine it.
2. The three low-order bits of the command address field must be zeros
in order for the CCW to be on a doubleword boundary. If the CCW is
not on a doubleword boundary or if the command address specifies a
location protected from fetching or outside the storage of a
particular user, the Start IIO instruction causes the status
portion of the CSW (channel status word) to be stored with the
program check or protection check bit on. In this event, the IIO operation is not initiated.
The CAW, located at storage location X'48', is displayed. Its format is: r , , KEY I 0000 I Command Address I o 3 4 4-7 B- 31
7 8 31 The protection key for all commands associated with start I/O. The protection key in the CAW is compared to a key in storage
whenever a reference is made to storage.
This field is not used and must contain binary zeros.
The command address field contains the storage address (in
hexadecimal representation) of the first CCW (channel command word) associated with the next or most recent Start I/O. Section 4. DEBUG Subcommands 265

DEBUG Subcommands-CSW csw Use the CSW subcommand to display at the terminal the contents CSW status word), as it existed at the time the
environment was entered. The format of the csw subcommand is:
of the
debug
r I CSW L- -.I 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 when an I/O interruption occurs. If I/O interruptions are
suppressed, the CSW is stored when the next Start Test I/O, or
Halt I/O instruction is executed.
2. Whenever an 1/0 operation abnormally terminates, issue the
subcommand. The status and residual count information in the
is very useful in debugging. Also, use the CSW to calculate
address of the last executed CCW (subtract eight bytes from
command address to find the address of the last ccw executed). CSW CSW the
the contents of the CSW are displayed at the terminal in hexadecimal
representation. Its format is:
r , I KEY 10000 I Command Address Sta tus Byte Count
L __ _ jl o 3 7 8 31 32 47 48 63 4_7 8-31
32-41 The protection key is moved to the CSW from the CAW. It shows
the protection key at the time the 110 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. field is not used and must contain binary zeros.
The command address contains a storage address (in hexadecimal
representation) that is eight bytes greater than the address
of the last CCW executed.
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.
266 VM/310 eMS Command Rnd Macro Reference