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3.6.3 Controlling Interrupts
Interrupt enable/disable control in a service call is accomplished by IPL manipulation. The IPL value in a service call is set
to the kernel mask level(OS interrupt disable level = system.IPL) in order to disable interrupts for the kernel interrupt han-
dler. In sections where all interrupts can be enabled, it is returned to the initial IPL value when the service call was invoked.
• For service calls that can be issued from only task context.
Task Service call issued
Service call processing
I flag
IPL
1
0 system.IPL system.IPL
1 0
0
1
0
Task Service call issued
Service call processing
I flag
IPL
0
0 system.IPL system.IPL
1 0
0
0
0
When the I flag before issuing a service call is 1.
When the I flag before issuing a service call is 0.
Figure 3.23 Interrupt control in a Service Call that can be Issued from only a Task