Set PWM on interrupt?

[RoGuE_StreaK]

Hi, trying to get back into PICs and attempting to convert some of my old code from using delays to using interrupts, but am having real issues getting even the basics working.
Can anyone give some pointers on how to change the duty of a PWM on timer interrupt, to fade an LED up and down? I can't even get that working, but if I can see an example that actually works I think I can sort myself out for the rest of my projects.

Here's a snippet example of things I've tried with no success

[PCM programmer]

You can use #int_timer2 to do this. It will interrupt at the same
frequency as the PWM, or at a multiple of that frequency (from 1 to 16).
Set the interrupt interval by setting the Postscaler parameter in the
setup_timer_2() function. See the CCS manual.

For example, you could have it interrupt once every 16 PWM cycles.
Then inside the #int_timer2 routine, you could change the duty cycle
with the set_pwm1_duty() function.

[RoGuE_StreaK]

Thanks PCM programmer, but I've already tried doing it that way. Also I wanted a different interrupt frequency, initially I didn't realise that the PWM was tied in with Timer2, so when I went through the wizard and set them both I didn't realise that the PWM setup was overwriting what I'd set for the timer2 interrupt earlier!

I had thought perhaps that there were issues with calling set_pwm(1/2)_duty() within an interrupt itself, so tried separating it out into a function call, so all the interrupt would have inside it was a call to a function that did all the work, but this method seems to have made no difference in my results.

The isrCount was just a test of doing something only every few interrupts rather than each time.

What I ultimately want to do is get sound playback happening, method being to cycle through an array of values at the sound's sample rate (eg. interrupt at 8kHz, set PWM to new value), whilst having the PWM frequency high enough that it doesn't cause unwanted noise. I figured also that I should set the Timer2 so that the PWM's duty cycle was natively as close to 255 as I could get, so I could set 8bit numbers directly to it without doing calculations first.

But as I said, I can't even get a simple "fade LED" system working via interrupts, and I can't see what I'm doing wrong.

The Roman Black 1-bt wav playback system in the code library only uses delays to set the playback rate, I'm going to be doing other operations with the PIC so wanted to use interrupts to get a consistent playback rate.

[PCM programmer]

I don't know if this is applicable to your project or not, but I made a
program that ramps the PWM duty cycle up and down continuously.
Look at pin C2 with your oscilloscope and you will see it.

[RoGuE_StreaK]

Thanks PCM programmer, that's what I'm after, something that has been proven to work by someone else that is triggered by the interrupt. I'll give it a go tonight.
From what I can see, at first glance it looks very similar to stuff I've already tried, but if it works, great I can use it as a starting point, if it doesn't then it should prove that I've got issues with either the chip itself or my breadboard, so I can find the cause of the problem rather than beating my head against a brick wall when the code itself might actually be fine.

PS. I don't have an oscilloscope, I'm just using an LED and the old mk1 human eyeball, so trying to get the timing at a rate that's discernable to a human.

[RoGuE_StreaK]

PS. I'm wondering what the difference/reasoning is for the two variables:

int8 duty_cycle; //outside the ISR
static int8 increment = TRUE; //inside the ISR

Why the different declaration styles in different locations? They both seem to be accessed the same way in the same function? Does it make "increment" only available within the ISR whereas "duty_cycle" is available anywhere perhaps?
I think I need to do some research on variable scope...

[RoGuE_StreaK]

OK this is bizarre; had no luck whatsoever with the above code, I've just spent a few hours experimenting, just decided to strip it right back and disable the interrupts, just testing a set_pwm1_duty by itself, and I came across the following behavior:

with
duty_cycle = 0;
and
set_pwm1_duty(duty_cycle);
I am getting a lit LED! Maybe about 50% brightness.

but if I say
set_pwm1_duty(0);
the LED doesn't light!!

So what the %@#& is going on here??!
If I set the variable "duty_cycle" to 0, or set it to 255, I'm still getting the same apparent brightness??


Clock is 20MHz, timer2 setup is
setup_timer_2(T2_DIV_BY_16,255,2);

Any thoughts would be greatly appreciated, as I've spent hours on this and haven't gotten anywhere, then find that even the most basic function isn't working as it should be!

PS. I've also swapped out the chips, so hardware doesn't appear to be part of the issue.

[Ttelmah]

What PIC?.
What compiler version?.
Have you actually tested that the output PWM frequency _is_ what you expect?.
You could get the symptoms being described, if timer2, was not being setup correctly.

Best Wishes

[PCM programmer]

Try a more simple program. This program reads a voltage from a
trimpot, and uses it to set the PWM duty cycle. The brightness of an
LED is controlled by turning the trimpot:
http://www.ccsinfo.com/forum/viewtopic.php?t=40007&start=1

[RoGuE_StreaK]

Seems at least part of the problem was a compiler issue. I was using 4.028, running a PIC18F2620. Have now tried 4.057, and the PWM works! I'm even getting "noise" out of my sound routine, definitely not the audio I'm after but it's definetely trying to do something that isn't just a tone, sounds like it's trying to use the sound array to some degree or other.

As I said, when setting duty cycle with a variable it didn't matter what the variable value was it would give the same result, but if I put actual numbers directly into the set_pwm1_duty() function then it would work. Now with 4.057 the variables are working as they should be, and seems that most of my failed attempts of code were actually correct, or near enough. Just wasn't compiling properly

Well it's now nearly midnight so I'm off to bed, I'll see if I can get this sucker operational over the weekend!

[Ttelmah]

Aargh!.

There for several years was a 'sticky thread' at the top of this forum, about V4. It is still on the forum, but has been allowed to move from the priority 'spot'.
Basically, V4, hardly worked for most chips, up to the late 03X versions.

This is particularly why several posters always ask for 'PIC', and 'Compiler version', when threads start.

Best Wishes

[RoGuE_StreaK]

Just a quick update, I now have recognisable audio output, the frequency needs a little bit of tuning but the system is now proven to definitely work. My initial code for the system seems like it was pretty-much spot-on, it was just because of the variable-to-pwm issue that it seemed like it was bad.

Now to figure out how to generate my own sample files and optimise the interrupt frequencies to suit...

[RoGuE_StreaK]

Possibly (probably?) a stupid question, but the original soundfile examples that I downloaded had the format of

[PCM programmer]

What PIC are you using ?

Is this being done in real hardware ?

What is your compiler version ?

[RoGuE_StreaK]

It's actually a few posts back; PIC18F2620
http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010284
64kB program memory, 4kB RAM, 1kB data eeprom.
4.057 compiler.

Real hardware, 20MHz crystal (no PLL, might change to 10MHz with PLL), hardware PWM with timer2 set to (div_by_1, 255, 1) (~19.5kHz? Highest setting I could figure out that kept 8bit resolution)

Sound is 16kHz mono 8bit, so timer0 set to interrupt @ ~32kHz, with routine being called every 2nd interrupt. Closest method/settings I could figure out to get close to 16kHz system.

I'll do some more tests tonight with it stripped back to just playing one soundfile in a loop, but from my last few experiments it appeared that the looping was occuring at the right time, but the last half of the time was empty of sound. Would then make a "glitch" sound and restart the loop, seemingly with different lengths of audible sound each time.