Example B.11. Vectored interrupt service routine

0x18    LDR pc,    [pc, #-0xff0]    ;  Load Vector into PC

;  .......................................................

vector_handler

       ;  Code to enable interrupt nesting

       STMFD r13!, {r12, r14}      ;  stack lr_irq and r12 [plus other regs used below, if appropriate]

       MRS r12, spsr               ;  Copy spsr into r12...

       STMFD r13!, {r12}           ;  and save to stack

;  Read from VICIRQStatus to determine the source of the interrupt

       MSR cpsr_c, #0x1f           ;  Switch to SYS mode, re-enable IRQ

       STMFD r13!, {r0-r3, r14}    ;  stack lr_sys and r0-r3

;  Interrupt service routine...

;  NOTE: ADS 1.2 requires preservation of 8-byte stack alignment with respect to all external

;  interfaces. See ADS 1.2 Developer Guide - Section 2.3.3

;  ...

       BL 2nd_level_handler        ;  this corrupts lr_sys and r0-r3

;  ...

;  Add code to clear the interrupt source;  Code to exit handler

       LDMFD r13!, {r0-r3, r14}     ;  unstack lr_sys and r0-r3

       MSR cpsr_c, #0x92            ;  Disable IRQ, and return to IRQ mode

       LDMFD r13!, {r12}            ;  unstack r12...

       MSR spsr_cxsf, r12           ;  and restore spsr...

       LDMFD r13!, {r12, r14}       ;  unstack registers

       LDR r1, =VectorAddr

       STR r0, [r1]                 ;  Acknowledge VIRQ serviced

       SUBS pc, lr, #4              ;  Return from ISR