lpcware

LPC1769 confusing timer settings (clockrate, matchregister)

Discussion created by lpcware Employee on Jun 15, 2016
Content originally posted in LPCWare by suckiden on Mon Dec 01 04:52:40 MST 2014
Hi everybody,

currently I am playing with the timer of the lpc. I want to generate an interrupt every 2us. As a starting point I used the periph_timer example.
It already has the following line of code in it:
timerFreq = Chip_Clock_GetSystemClockRate();

it returns 96 000 000 so I know my processor and timer are both running at 96MHz
Than I tried a bit of math: 1/96 000 000 = 10,416...ns
(desired value) 2000ns / 10,416.. ns = ~192 so I set the Prescaler to this value and Match value to 1 so every 2us an interrupt should occur.
I measured the output of the board LED0 and got a value of 16us not really what I expected.
I played a bit with the Prescale values an figured out that with 24 I get the right result. Could it be that the real timer clock is 12MHz (96MHz/8) ?
When yes, where can I find this settings?

best regards Suckiden

Outcomes