User Manual

EP7309/11/12 User’s Manual - DS508UM4 4-3
Copyright Cirrus Logic, Inc. 2003
Interrupt Controller
44
4
bne nextstatuscheck ; not the timer - moving down the IRQ routine
mov r2, #0x0
strb r2, [r0,#0x0] ; setting PA0-8 low
mov r2, #0xFFFFFFFF
str r2, [r0,0x06C0] ; Write to TC1EOI register - clear interrupt
; ........ code...........
subs pc, lr, #4 ; Return from interrupt to pending instruction
;
Operational Overview
Once an exception occurs, the ARM720T will attempt to complete the current
instruction (except for a system reset) and will then identify the interrupt type. The
interrup t vector tab le, already loaded by the system software contains a reference or
address of the specific interrupt routine for each type of exception identified by the
processor. The CPU will jump to the appropriate routine for servicing of the interrupt.
The vector table for all interrupt types is as follows:
Within each routine for each inter rupt type created by the system software, the
specific interrupt can be determined by examining any one of the three status
registers. After an action is taken, a w rite to the appropriate “End of Interrupt”
register must be issued to clear the interrupt status register to prevent re-entry an d an
endless loop.
For several i nterrupts occurring simultaneously, the pre-determined priority bas ed on
type of interrupt will cause the highest interrupt priority to execute first and queue
any remaining interrupts. In terrupts of the same type that occ ur simultaneously
simplyrequiresystemsoftwaretocheckallpossibleinterruptsforthespecifictype.
Table 4-2: Vector Addresses by Interrupt Type
Interrupt Vector Address
Reset 0x0
Undefined Instruction 0x4
Software Interrupt (SWI) 0x8
Prefetch Abort (Instruction fetch) 0xC
Data abort (Data access) 0x10
IRQ (normal interrupt) 0x18
FIQ (fast interrupt) 0x1C