The specified device is checked for an active file. If no active file
is found, cc=2 is set. Otherwise, the file is backspaced one record and
the record is given to the user as in subcode 1'0000'. If the file is
already positioned at the first record, the first record is given to the
user. Subcode X'001C' Rx = virtual address of a 12-doubleword buffer
Ry = virtual spool reader address
Processing is the same as Subcode 1'0008', except
spool files, as identified by the SFBMON flag is
handled. Subcode 1'0020' Rx = start address of full page virtual buffer
Ry = virtual spool reader address
Processing is the same as Subcode X'OOOO', except
spool files, as identified by the SFBMON flag in
handled. Subcode X'OFFF' Rx = virtual address of a 252-byte buffer
Ry = spool file ID number that only monitor
SFBFLAG2, can be
that only monitor
SFBFLAG2, can be
If Ry is nonzero, the spool input chain is searched for a file with a
matching ID nu.ber: If none is found or if one is found that is owned
by a different virtual machine, cc=2 is set. The chain search is
continued from the file that was found, or from the anchor if Ry is
zero, for the next file owned by the caller, independent of file type,
class, INUSE flag, etc. If none is found, cc=1 is set. Otherwise, the SPBLOK and the first record of the file (generally, the TAG) are copied
to the caller's virtual storage buffer.
Input/output operations to a direct access device, of the type used by CMS, can be performed from a virtual machine using DIAGNOSE code X'18'. No I/O interrupts are returned by CP to the virtual machine; the DIAGNOSE instruction is completed only when the READ or WRITE com.ands associated with the DIAGNOSE are completed. The Rx register contains
the virtual device address of the direct access device. The Ry register
contains the address of a chain of CCWs. The CCW chain must be in a
standard format that CP expects when DIAGNOSE code X'18' is used, as
shown below. Register 15 must be loaded by the user with the number of
READs or WRITEs in the CCW chain.
1-56 IB! V8/370 System LogiC and Problem Deter.ination--Volu.e 1

A typical CCW string to read or write two SOO-byte records is as
follows:
SEEK,A,CC,6 SET SECTOR (not used for 2314/2319) SRCH,A+2,CC,5 TIC,*-8,0,0 RD or WRT,DATA,CC+SILI,800 SEEK HEAD,B,CC,6 (omitted if HEAD number unchanged) SET SECTOR SRCH,B+2,CC,5 TIC,*-8,O,0 RD or WRT,DATA+800,SILI,800 A SEEK and SRCH arguments for first RD/WRT B SEEK and SRCH arguments for second RD/WRT The condition codes and completion codes returned are as follows: cc=O I/O complete with no errors cc=l Error condition. Register 15 contains one of the following:
R15=1
R 15=2
R15=3
R15=4
R15=5
Device not attached
Device not 2319, 2314, 3330, 3340, or 3350 Attempt to write on a read-only disk
Cylinder number not in range of user's disk
Virtual device is busy or has an interrupt pending
cc=2 Error condition. Register 15 contains one of the following:
R15=5
R15=6
R15=1
R15=8
R15=9
R 15=10 R15=11
R15=12
Pointer to ccw string not doubleword-aligned. SEEK/SEARCH arguments not within range of user's
storage READ/WRITE CCW is neither Read (06) nor Write (05) READ/WRITE byte count=O READ/WRITE byte count greater than 204S READ/WRITE buffer not within user's storage
The value in R 15, at entry, w-as not a positive number froB 1 through 15. or was not large enough for the
given CCW string.
Cylinder number on seek head was not the same number as
on the first seek.
cc=3 Uncorrectable I/O error:
R15=13 CSW (8 bytes) returned to user Sense bytes are available if user issues a SENSE com.and Code == Clg!: Er!:.Q!: Cylinders Execution of DIAGNOSE code X'1C' allows a user with privilege class F to
clear the error recording data on disk. The DftKIOEFft routine performs the clear operation. The register specified as Rx contains a one-byte
code value in the low-order byte as follows:
Code Xt01' 1'02' Function Clear-aid reformat all error recording, leaving any frame records intact
Clear and reformat all error recording cylinders, erasing
both frame records and error records
CP Introduction 1-51