touble with a time calculation

[longpole001]

hI GUYS , using the code by steve seems to work , a small change cos i use EL1 values to show the current time value , so any changes that change the EL1 values in the calculating the EL2 , is not possible so i need to copy the values of EL1 to EL3 , then use EL3 as a temp group

I am trying to disable the interupt whilest in the ISR subroutine , before the copy of EL0 to EL1-3 , then re -enable interrupt after ,

but i get a interrupt priority state not found error when compile atm

[richard]

it serves no purpose to stop the isr from within the isr , its a waste of time copying the el vars to a buffered copy inside the isr .
time in your case is in essence a multi byte var , the value is volatile and cannot be guaranteed outside the isr when the isr is running.
the correct procedure is
disable isr
copy bytes to buffer
enable isr
do your subtraction