ST90158P9C6 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST90158P9C6

8/16-BIT MCU FAMILY WITH UP TO 64K ROM/OTP/EPROM AND UP TO 2K RAM

STMicroelectronics 

ST90158 - INTERRUPTS

ARBITRATION MODES (Cont’d)

End of Interrupt Routine

The iret Interrupt Return instruction executes

the following steps:

– The Flag register is popped from system stack.

– If ENCSR is set, CSR is popped from system

stack.

– The PC high byte is popped from system stack.

– The PC low byte is popped from system stack.

– All unmasked Interrupts are enabled by setting

the CICR.IEN bit.

– The priority level of the interrupted routine is

popped from the special register (NICR) and

copied into CPL.

– If ENCSR is reset, CSR is used instead of ISR,

unless the program returns to another nested

routine.

The suspended routine thus resumes at the inter-

rupted instruction.

Figure 23 contains a simple example, showing that

if the ei instruction is not used in the interrupt

service routines, nested and concurrent modes

are equivalent.

Figure 24 contains a more complex example

showing how nested mode allows nested interrupt

processing (enabled inside the interrupt service

routinesi using the ei instruction) according to

their priority level.

Figure 24. Complex Example of a Sequence of Interrupt Requests with:

- Nested mode

- IEN set to 1 during the interrupt routine execution

Priority Level of

Interrupt Request

0

1

INT 0

CPL=0

INT0

CPL6 > CPL3:

INT6 pending

INTERRUPT 0 HAS PRIORITY LEVEL 0

INTERRUPT 2 HAS PRIORITY LEVEL 2

INTERRUPT 3 HAS PRIORITY LEVEL 3

INTERRUPT 4 HAS PRIORITY LEVEL 4

INTERRUPT 5 HAS PRIORITY LEVEL 5

INTERRUPT 6 HAS PRIORITY LEVEL 6

2

INT 2

INT 2

INT 2

CPL=2

CPL=2 INT6

CPL=2

3

ei

INT 3

CPL=3 INT2

INT2

4

INT3

ei

INT 4

INT4

CPL2 < CPL4:

CPL=4

5

INT 5

Serviced just after ei

ei

ei CPL=5

6

ei

INT5

INT 4

CPL=4

INT 5

CPL=5

INT 6

CPL=6

7 MAIN

CPL is set to 7

MAIN

CPL=7

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