Software PWM minimal frequency

[msawicki-poland]

I use 2.3.0 pi4j library and Kotlin and I created pwm config like this:

fun pwmConfig(pi4j: Context): PwmConfig = Pwm.newConfigBuilder(pi4j)
        .address(27)
        .pwmType(PwmType.SOFTWARE)
        .provider("pigpio-pwm")
        .initial(0)
        .shutdown(0)
        .build()

and I run pwm like this:
pwm.on(4.0, 2)
On osciloscope I found that it generates 10Hz not 2Hz. Why I cannot run pwm for 1-9Hz?

[taartspi]

PWM software uses the Pigpio library https://abyz.me.uk/rpi/pigpio/index.html That on() method calls gpioSetPWMfrequency in that library. Their doc has a table showing possible frequencies. That details says the 'sample rate' is used to determine the chart value defining minimum freq, apparently the sample rate resulted as 10 the lowest possible . I tested freq of 18 results in the actual freq being 20. I do not see that we support setting the sample rate (gpioCfgClock) All that said, we already recognize the desired software frequency may not be possible :
/**
* Turn the PWM signal [ON] using a specified duty-cycle (%)
* at the pre-configured frequency (Hz).
*
* @param dutyCycle The duty-cycle value is a decimal value that represents the
* percentage of the ON vs OFF time of the PWM signal for each
* period. A value of 50 represents a duty-cycle where half of
* the time period the signal is LOW and the other half is HIGH.
* The duty-cycle range is valid from 0 to 100 including factional
* values. (Values above 50% mean the signal will remain HIGH more
* time than LOW.)
* @param frequency The desired frequency value in Hertz (number of cycles per second)
* that the PWM signal generator should attempt to output. Please
* note that certain PWM signal generators may be limited to
* specific frequency bands and may not generate all possible explicit
* frequency values. Immediately after calling this method, you can
* check the 'Pwm::actualFrequency()' or 'Pwm::getActualFrequency()'
* properties to determine what frequency the PWM generator actually
* applied.
* @return returns this PWM instance
* @throws IOException if fails to communicate with the PWM pin
*/
This info is in the java docs, I will ask this question be converted to a work item and update the web pages with this caution. @FDelporte Sir, can you convert this to a DOC work item and I will update the web pages to include this caution.

[BetterB0y]

So settings even 8kHz isn't possible, because of lack of sample rate setter?

[taartspi]

i assume you mean 8 hz, not 8KHz Correct, appears 8 HZ will have an actual freq of 10 Hz, If you can spare using a hardware PWM it appears to do what you want. I didn't connect a my scanaquad to watch the line but looks like the LED is flashing at that slow rate.

[BetterB0y]

I meant 8 kHZ. We only achived max 2 kHZ. I think in documentation we found that max we can do 8 kHZ of software pwm

[taartspi]

your test case used 2 Hz, I did not realize you were starting a different question. I would suggest use the step written in the javaDoc to set the freq and inspect its actual value by calling the method'Pwm::getActualFrequency() If actual is 8Khz and signal measurement is far less, I suspect this is what the web pages mentions that soft pwm is not accurate compared to hw pwm. "software version cannot achieve precise or particularly fast frequencies."