ST20-GP1 datasheet(33/116 Pages) STMICROELECTRONICS

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ST20-GP1

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The interrupt controller receives external interrupt requests and makes an interrupt request to the

CPU when it has a pending interrupt request of higher priority than the currently executing interrupt

handler.

The Pending register is mapped onto two additional addresses so that bits can be set or cleared

individually.

Set_Pending (address ‘interrupt base address + #84’) allows bits to be set individually. Writing a

‘1’ in this register sets the corresponding bit in the Pending register, a ‘0’ leaves the bit unchanged.

Clear_Pending (address ‘interrupt base address + #88’) allows bits to be cleared individually.

Writing a ‘1’ in this register resets the corresponding bit in the Pending register, a ‘0’ leaves the bit

unchanged.

Note, if the CPU wants to write or clear some bits of the Pending register, the interrupts should be

masked (by writing or clearing the Mask register) before writing or clearing the Pending register.

The interrupts can then be unmasked.

Exec register

The Exec register keeps track of the currently executing and pre-empted interrupts. A bit is set

when the CPU starts running code for that interrupt. The highest priority interrupt bit is reset once

the interrupt handler executes a return from interrupt (iret).

The Exec register is mapped onto two additional addresses so that bits can be set or cleared

individually.

Set_Exec (address ‘interrupt base address + #104’) allows bits to be set individually. Writing a ‘1’

in this register sets the corresponding bit in the Exec register, a ‘0’ leaves the bit unchanged.

Clear_Exec (address ‘interrupt base address + #108’) allows bits to be cleared individually. Writing

a ‘1’ in this register resets the corresponding bit in the Exec register, a ‘0’ leaves the bit unchanged.

Pending

Interrupt controller base address + #80

Read/Write

Bit

Bit field

Function

PendingInt0

Interrupt 0 pending bit.

PendingInt1

Interrupt 1 pending bit.

PendingInt2

Interrupt 2 pending bit.

PendingInt3

Interrupt 3 pending bit.

PendingInt4

Interrupt 4 pending bit.

Table 5.4 Pending register format

Exec

Interrupt controller base address + #100

Read/Write

Bit

Bit field

Function

Interrupt0Exec

Set to 1 when the CPU starts running code for interrupt 0.

Interrupt1Exec

Set to 1 when the CPU starts running code for interrupt 1.

Interrupt2Exec

Set to 1 when the CPU starts running code for interrupt 2.

Interrupt3Exec

Set to 1 when the CPU starts running code for interrupt 3.

Interrupt4Exec

Set to 1 when the CPU starts running code for interrupt 4.

Table 5.5 Exec register format

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