DOUBLEWORD SAVE BLOCK Read Address I (2) TIC Address Unused Read Data Area I I (3) !odified CCW (4) TIC to RCWTASK Real Read CCW Real TIC CCW Return to DKKCCW module via SVC 12. SCHEDULING CP lND VIRTUAL I/O OPERATIONS AND INTERRUPTION HANDLING Entry to process CP generated I/O. Flag the IOBLOK as a CP generated
event. Initiate I/O if path to real device is free (available). If
not, queue the IOBLOK and return to caller. Entry to process I/O for virtual aachine I/O operations. !ark IOBLOK as not CP initiated. Save V!BLOK address. If path to the VDEVBLOK or the VDEVBLOK is busy queue the IOBLOK and return to caller. If available status, start the I/O and return to caller. DMKIOS, IOBSTART ---rl-I/o--request has not been reset, save the address of the active IOBLOK and set device busy. If the device is being reset, unflag
scheduled device and scheduled control unit. Stack the IOBLOK and
restart the device. IOS§!Q Set the subchannel path busy and chain the active IOBLOK fro. the RDEVBLOK. DMKIOS, IOSSIO CAW and issue the SIO. Check SIO co.pletion.
Returned condition code sets sequel action.
cc = 0 indicates successful start
cc = 1 CCW stored, initiate sense operation
cc = 2 Busy condition, retry or requeue IOBLOK cc = 3 Fatal error (not operational), stack the IOBLOK and return to
caller
CP Kethod of Operation and prograa Organization 1-195

DKKIOSHA point for halting a device. If device is not active, return to
caller. If IOBLOK active, reset the IOBLOR to halt the device and
mark the device reset in RDEVBLOK. DKKIOS, IOS10KI path is busy with a burst mode operation, stack the IOBLOK to halt the operation when the channel path becomes available.
Return to caller. DI1KIOSIN from I/O new PSi. Check old PSi. If problem mode, save
processor status in the VMBLOK. DMKSCNRN Locate RCHBLOK, RCUBLOK, and RDEVBLOKs for interruption unit. DMKVIOIN ---Process dedicated channel interruption condition. If control unit
end or channel available interruption occurs, restart the operation,
if interruption does not occur stack it. DMKIOSIN IOBLOK is not active on RDEVBLOK interruption. call DftKIOS. IOSENSE Schedule sense operation, then go to dispatcher. DMKIOS, For PCI or CE interruptions, copy and stack the IOBLOK. Process PCI or CE interruptions, if related to local graphic device
or nondedicated TP line. DMKIOS, DOSERSE For split seek complete interrupt, rechain the seek and reschedule
operations. DMKSTKIO -- Stack IOBLOK and restart any units freed by the interruptions. DMKDSPCH, DMKDSPA ---rj-the syste.-Iock is held or is available. exit to the main entry of
the dispatcher, DMKDSPCH. Otherwise, exit to DftKDSPA to try to
redispatch RURUSER. TERMINAL CONSOLE I/O CONTROL, START/STOP, 3210, 3215, AND OTHERS DMKCRSEN ---Per-unstacked CPEXBLOK, on enable or disable function, check current
status of the current real device and set flag in RDEVFLAG. Build CONTASK and IOBLOK. Issue SIO for enabling or disabling function and check return. DP.lKDSPCH dispatcher.
1-196 IBP.l VM/310 System Logic and Problem Determination--Volume 1