Hi,
entire code is attached, minimum measured frequency is defined only maximum number of overflows.
It worked, however, I have not seen it for, really will not lie, for years.
Yes, it is for different MCU but principle....
The code only measures frequency without measuring duty cycle.
1)
- a) The first idea of measuring both pulse parts was described previously.
- b) Probably I can add that the type of edge can be also investigated by interrupt flag, without enabling interrupt, at two independent pins connected also to input signal.
- c) The issue you have is to make a compromise for maximum precision of the 1000Hz frequency and amount of overflows for 10Hz frequency from timer prescaler point of view.
- d) You should perform your own analysis a decide for timer setup as presented in the example, file main.c:
* Detailed Description:
* - It mesure frequency at PT1 by means of ECT module.
* - The measaurement is sensitive on rising edges so duty cycle has no affect
to the measurement
* - Constants:
BUSCLOCK
MAX_OVERFLOWS
TIMER_PRESCALLER
must be defined
* - MAX_OVERFLOWS determines minimum mesurable frequency.
It is max. allowed number of overflows. When overflows counter reaches
this value it the flag FREQUENCY_TOO_LOW is set. The message
PERIOD BETWEEN TWO EDGES IS TO WIDE is then sent sent to the PC through
SCI0. This value gives time interval:
T = TIMER_PRESCALER * MAX_OVERFLOWS * 65536 / BUSCLOCK
For example:
- TIMER_PRESCALER = 1
- MAX_OVERFLOWS = 1000
- BUSCLOCK = 8000000Hz
T = 1 * 1000 * 65536 / 8000000 = 8,192s => f=0.122Hz
* - TIMER_PRESCALER = { 1,2,4,8,16,32,64,128} - smaller values give more
precise values but it generates timer overflow more frequently
... for example....
2) The issue I see is duty cycle measurement for small a large duty cycles in the first method. Because of this I would try to solve second method.
3) Another possibility and approach is to connect input signal to two different timer inputs and calculate period from rising edges from one channel including duty provided by interrupt on different channel for falling edge. However, it also requires study and tests.
incomming signal |^^^^^^^^^^^^^^^|_____________________________________________|^^^^^^^^^^^^^^^|____
ICx (rising edges) |<----period measured by ICx, P= f(TCx_old, TCx_new,ovfs)------------->|<----period-----
ICy (falling edges) |- event which stores TCy and num. of ovfs to be able to calc. duty |- again
4) Your task is really not simple and will require a lot of test and modifications. Probably there is also much simpler solution but not going to my mind now.
Best regrads,
Ladislav
Hi,lama
I have a idea for this problem. I use the interrupt of Timer0 IOC0 and IOC3. IOC3 is for input capture and IOC0 for output compare. The timer base frequency is 200K. If I add the compare value at IOC0 interrupt , then I can generate a 10us interrupt. I will deal with the output compare using the period interrupt(10us) for 10hz~1000Hz. The problem is when I set the different priority it will meet some problem. If I set the same priority it works well. You can see the problem below:
I want to set the priority of IOC0 is higher than IOC3, what can I do?
