DMSFNS: In the case where the specified disk is replacing a currently accessed disk, closes any open files belonging to the duplicate disk. Verifies the parameters remaining on the command line. DMSALU: Releases any free storage belonging to the duplicate disk via a call-to DMSFRE. Also, clears appropriate entries in the ADT for use by the new disk. (Called as the first instruction by DftSACF) Reads, fro. the
Master File Directory, QMSK, and the QQftSK for the specified disk; also, DMSACM updates the ADT for the specified disk using information from the
MFD. DMSACF: Reads into storage all the FST blocks associated with the specIfied disk. DMSACC: Handles error processing or processing required to return control to DMSINT. Handling I/O Operations CMS input/output operations for disk, tape, and unit record devices are
always synchronous. Disk and tape I/O is initiated via a privileged
instruction, DIAGNOSE, whose function code requests CP to perfor.
necessary error recovery. Control is not returned to CBS until the
operation is complete, except for tape rewind or rewind and unload
operations, which return control immediately after the operation is
started. No interruption is ever received as the result of DIAGNOSE I/O. The CSW is stored only in the event of an error.
Input/output operations to a card reader, card punch, or printer are
initiated via a normal START I/O instruction. After starting the
operation, CMS enters the wait state until a device end interruption is
received frem the started device. Because the I/O is spooled by CP, CBS does not handle any exceptional conditions other than not ready,
end-of-file, or forms overflow. eMS input/output operations to the terminal may be either synchronous
or asynchronous. Output to the terminal is always asynchronous, but a
program may wait for all terminal input/output operations to complete by calling the console wait routine. Input from the terminal is usually
synchronous but a user may cause CMS to issue a read by pressing the
attention key. A program may also asynchronously stack data to be read by calling the console attention routine. UNIT RECORD I/O PROCESSING Seven routines handle I/O processing for CftS: DMSRDC, DftSPUR, and DBSPRT handle the READCARD, PUNCH, and PRINT commands and pass control to te
actual I/O processors, DMSCIO (for READCARD and PURCH) or DftSPIO (for PRINT). DMSCIO and DMSPIO issue the 510 instructions that cause I/O to
take place. Two other routines, DftSIOi and DMSITI, handle
synchronization processing for I/O operations. Figure 18 shows the
overall flow of control for I/O operations.
2-94 IBM VM/370 System Logic and Program Determination--Voluae 2
DMS DMS DMS RDC PUN
PRT I - 1"""- I , I I I I Channel DMSCIO DMSPID - -+ SIO / DMSIOW I -- -
- I- I I - I I -.,.. - -- I I Figure 18. Flow of Control for Unit Record I/O processing DMSITI I The following are more detailed descriptions of the flow of control for
the read, punch, and print unit record control functions. Initializes block length and unit record size. Initializes areas to read records. Issues an 510 command to read a record. Sets the wait
old PSi from NUCON. read I/O is complete.
bit for the virtual card reader and load the I/O This causes CMS to enter a wait state until the DMSITI: Ensures that this interrupt is for the virtual reader. If not, the--I/O old PSi is loaded, returning CftS to a wait state. If the
interrupt is for the reader, DKSITI resets the wait bit in the I/O old PSi and loads it, causing control to return to Places the symbolic name of the interrupting device in the PLIST and passes control to the calling routine. ChecKs for SENSE information
necessary.
and handle I/O errors, if CMS Method of Operation and Program Organization 2-95
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