critical.gcc.s

@******************************************************************************
@
@ Useful functions.
@
@******************************************************************************
.global  DisableInterrupts
.global  EnableInterrupts
.global  StartCritical
.global  EndCritical
.global  WaitForInterrupt

@*********** DisableInterrupts ***************
@ disable interrupts
@ inputs:  none
@ outputs: none
DisableInterrupts:
        CPSID  I
        BX     LR

@*********** EnableInterrupts ***************
@ disable interrupts
@ inputs:  none
@ outputs: none
EnableInterrupts:
        CPSIE  I
        BX     LR

@*********** StartCritical ************************
@ make a copy of previous I bit, disable interrupts
@ inputs:  none
@ outputs: previous I bit
StartCritical:
        MRS    R0, PRIMASK  @ save old status
        CPSID  I            @ mask all (except faults)
        BX     LR

@*********** EndCritical ************************
@ using the copy of previous I bit, restore I bit to previous value
@ inputs:  previous I bit
@ outputs: none
EndCritical:
        MSR    PRIMASK, R0
        BX     LR

@*********** WaitForInterrupt ************************
@ go to low power mode while waiting for the next interrupt
@ inputs:  none
@ outputs: none
WaitForInterrupt:
        WFI
        BX     LR