The 2880 analysis routine handles channel data checks, interface
control checks, and channel control checks.
Termination code 3 (system reset) is not set in the ECSW because the 2880 channel does not issue system reset to the devices. Retry codes of
o to 5 are possible •. Note: There are several catastrophic conditions under
termination flag can be set, in the 2880 analysis routine. • The channel did not complete the logout. • The CSW is not reliable.
which the CP
They are: • The unit address in the I/O interruption device address field is not correct. Only a channel check record is needed if the channel has recognized
an internal error and has recovered from it without any daaage. 10 recovery action is necessary in these cases. If the channel address in the I/O interruption device address field
does not aatch the channel address in the logout, a CP termination
condition exists.
If the channel vas doing a scan and the unit control word had a
parity check a CP termination condition exists. If there was no parity
check, there vas no damage during the scan and only a channel check
record is required.
Depending on the sequence the channel has entered, the termination
and sequence codes are set; command address, unit address, and unit
status validity is determined; and the sequence code is set valid. The ECSW field in the channel check record is moved into the IOERBLOK, if
one exists.
Before returning to the channel control subroutine, the 2880 routine moves the I/O extended logout into the channel check record and sets the I/O extended logout area to ones. ERROR RECORDING INTERFACE FOR VIRTUAL MACHINES The error recording interface provides a means of recording errors
encountered by operating systems running in a virtual aachine under V8/370. If the virtual operating system is V8/370, it aust be the
Release 2.0 version or later. An SVC 76 issued by a virtual machine is
used to signal VM/370 that error recording is required. The SVC interruption handler in DMKPSA examines general registers 0 and 1 to
determine if valid parameters have been passed. If valid paraaeters are
not found, the SVC is reflected back to the virtual machine and no
recording takes place. If valid parameters are passed, a pageable
routine (DMKVER) processes the error record. DMKVER validates the record passed by the virtual aachine. If
invalid conditions are found, no recording takes place. Control is
returned to the SVC interruption routine in D8KPSA to reflect the SVC to
the virtual machine as an SVC interruption. The action taken by the
virtual machine is dependent on the operating system running in the
virtual machine, not V8/370. If the record is valid, it is aodified by
changing virtual information to real. The actual recording is accomplished by using existing aodules in DMKIOE and DMKIOF. CP Introduction 1-161

Control is then returned to the instruction following the SVC 76
rather than reflecting the SVC. This eliminates the duplication of error recording in VM/370 and the operating system in the virtual machine. If DMKYER determines that the recording represented a permanent I/O error, a message is sent to the primary system operator. ERROR RECORDING AND RECOVERY The error recording facility is made up of four modules. (DMKIOE) is resident and the other three (DMKIOC, DMKIOF, are pageable. One module and DMKIOG) The error recording modules record temporary errors (statistical data
recording) for CP generated I/O except for DASDs with a buffered log.
The error recording routines record: unit checks, statistical data
counter overflow records, selected temporary DASD errors, machine
checks, chanLel checks, and hardware environmental counter sense data on
the error recording cylinders of the system resident device in a for.at
suitable for subsequent processing by the CPEREP command (DMSIFC). The
recorder asynchronously updates the statistical data counters for
supported devices. The recorder also initializes the error recording
cylinders at IPL if they are in an unrecognizable format. When the recorder is entered from DMKIOS, it is entered at DMKIOERR. This entry is used for unit checks and channel data checks. A test is
.ade of the failing CSW (located in the IOERBLOK) to see if the error
was a channel error. If it was, control is passed to the routine for
recording channel checks.
The IOERBLOK sense data, IOBLOK flags, and VMBLOK privilege class are
examined to determine if the error should be recorded. ERROR RECORD WRITING After an error record is formatted, it is added to the error recording
cylinder using DMKRPAGT and DMKRPAPT. The error recording cylinders
have page-sized records (4096 bytes). Each page contains a header (8
bytes) which signifies: the cylinder and page number of the page (4
bytes), the next available space for recording within page (2 bytes), a
page-in-use indicator (1 byte), and a flag byte. Each record within the
page is recorded with a 4-byte prefix.
If an error record is too large to be added into a page, a new page
is retrieved, updated with record, and placed back on the error
recording cylinder with the paging routines.
From two to nine cylinders are used for error recording; errors are
recorded in the order in which they occur. The cylinders that are used
for error recording are specified by the installation or system programmer at system generation time. If the error recording cylinders
become 90 percent full, a message is issued to the operator using DMKQCNWT to warn him of the condition. If the cylinders beco.e full,
another message is issued to inform the operator and recording is
stopped. On the 3031, 3032, and 3033 processors, frame records are read from the SRF device and written on the error recording cylinders during
initialization if no records exist after a CPEREP CLEARF operation.
1-162 IBM VM/370 System Logic and Problem Determination--Volu.e 1