touble with a time calculation

[richard]

steve has the right idea for the math but since el1/el2 vars can be updated via the isr at any time during the calcs the results will vary.

statisticly it will fail about 4-5 times per hundred calcs based on :-
I think chances of failure are 1/60+1/60+1/100+1/24 I might be wrong about the stats

[EarlyBird2]

If isr affects EL1 vars create Temp_EL1 vars at the start of the routine and use these for the calculation.

[richard]

won't work . the isr can change the values as u copy them to the temp vars ,been there done that

[EarlyBird2]

Ok some problems do not have an answer.

Bye

[richard]

only solution I know is to disable isr and copy vars to a buffer then enable isr and then perform calcs on the buffered data.
it may mean the odd lost interrupt / whats worse incorrect calcs or missed ints
only the designer can make that call .