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Service Calls from a Handler That Caused an Interrupt during Handler Execution
Let u
s think of a situation in which an interrupt occurs during handler execution (this handler is hereinafter referred to as
handler A for explanation purposes). When task switching is called for as a handler (hereinafter referred to as handler B)
that caused an interrupt during handler A execution issued a service call, task switching does not take place during the exe-
cution of the service call (ret_int service call) returned from handler B, but is effected by the ret_int service call from han-
dler A (See Figure 3.13).
ret_int
ret_int
iset_flg
I
nterrupt
Interrupt
TaskA
Interrupt handler A
Save Registers
Service call processing
OS
Restore Register
SP <= User
Restore Registers
Task selection
TaskB
Save Registers
SP <= System
Interrupt handler A
Restore Register
Figure 3.13 Processing Procedure for a service call from a Multiplex interrupt Handler