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Contents
INTERRUPTS AND CYCLE STEAL REQUESTS 4-1
INTERRUPTS . . . . . . . 4-1
Local Storage Register Stack 4- 2
Interrupt Levels . . . . . . 4-3
Interrupt Level 0 4-3
Interrupt Level 1-Disk and Diskette 4-3
Interrupt Level 2-Communications and
Fixed Interval Timer 4-3
Interrupt Level 3 4-3
Interrupt Level 4 4-3
Interrupt Level 5 4-3
Main Program Level Interrupt. 4-3
Interrupti Cycle Steal Priority
Encode and LSR Selection 4-4
MSP Set Interrupt Level 5 . 4-5
CONTROL PROCESSOR AND MAIN STORAGE
PROCESSOR COMMUNICATION 4-6
CONTROL PROCESSOR AND CHANNEL
COMMUNICATION. . . . . . . . . . 4-7
Contents for Interrupts and Cycle Steal Requests
Interrupts and Cycle Steal Requests
INTERRUPTS
The control processor executes instructions one Priority Interrupt Level or Function If the control processor is not working with' All interrupt levels use the same processor
at a time; one instruction is followed by the Cycle Steal interrupts, it is executing instructions on the condition register; therefore, the processor
next sequential instruction. This sequence of Request main program level. condition register must be saved when entering
instructions can be changed by executing a Interrupt 0 Machine check routines an interrupt level and then restored when
branch or jump instruction. The sequence can Each interrupt level and the main program level leaving the interrupt level. This process ensures
also be changed by passing control from (1) 2 Burst cycle steal Disk data movement has a set of re,gisters in the local storage that the contents of the processor condition
one interrupt level to another interrupt level of register stack. Interrupt level 0 and the main register are correctly associated with the
higher priority, or (2) to the main program level. 3(note) Base cycle steal 5251 Display Station program level use the same set of work interrupt level in process. (If the interrupt level
registers. program does not change the processor
The control processor uses the main program 4 Interrupt 1 Disk data I/O supervisor; condition register, the save/restore process is
level, six levels of interrupts, and two levels of diskette data movement Each interrupt level and the main program level not necessary.)
cycle steal requests to interrupt the control has the following set of local storage registers:
storage program; the priority is set by 5 Interrupt 2 Communication line 1; When the port senses an interrupt request,
hardware. Interrupt level 0 has the highest fixed interval timer