#STM8 COSMIC PWM EXAMPLE SOFTWARE#
#STM8 COSMIC PWM EXAMPLE CODE#

This stops the C compiler kicking up a fuss.Д®xtern void timer_interrupt(void) Now, we add a reference to that routine to the table itself. Now we know that, we can do some work.ДЇirst, we edit the interrupt table, adding an 'extern' reference to our assembler routine. Variables have an underscore, so 'my_var' becomes '_my_var'. In my case, I was interested in the names of functions and global variables, so I compiled up a quick program with one global variable and one function.ДЇor a function name of 'MyFunction', the actual label generated in the assembler (and thus the format of the name we need to use) is 'f_MyFunction'.

#STM8 COSMIC PWM EXAMPLE CODE#

So, how do we make our assembler code work with existing 'C'? Well, first thing to do is take a trivial program and compile it in the 'Debug' folder of the project you'll find the generated assembler code (for example, main.ls) - look at this and you can find out how the name mangling works. As an idea of how fat C code is, the equivalent C routine had a worst case of 500 cycles. I should be able to streamline it a bit (or even a lot), but I doubt it's ever going to be able to run at 64kHz. So, 32kHz it is, and my interrupt is gonna use around 1/3 of total CPU all by itself.

My first cut interrupt routine has a 'worst case' of just over 200 cycles, so that cuts out 64kHz if we want to do anything clever elsewhere.

#STM8 COSMIC PWM EXAMPLE SOFTWARE#

Indeed, due to the way my software works, I can only generate up to 16kHz with a 32kHz clock, and there's a really coarse granularity on the high end - it's basically not much cop above 1kHz or so, around 2 octaves up from middle C.ДЄnyway, 512 cycles is not much to play with. Bearing in mind that human audio range peaks at ~20kHz, we'd probably like to be using a 32kHz or better clock. The prescaler value gives us, direcly, the number of clocks we have to play with at that frequencyДЄnd so on. The clock of the disco board runs at up to 16 MHz, so we can work out easily enough what frequencies we can call our hypothtical interrupt at. Now, we need to work out how much we can do, and how long we have to do it. How we go about varying the frequencies is another matter, but the main problem is doing 8 channels - I could do 4 with just the timers, but 8 is pretty tricksy.Д«asically, the approach I'm taking is to use a timer firing at a regular frequency, and do additive synthesis to make the final output volume (I'll initially be using a simple approach with no fading of the 8 pseudo-oscillators, so the maximum output volume is 8 that lets us get away with a 4 pin R-2R DAC (but more on that later). What I want to do is 8 channels of audio-range square waves, at differing and varying frequencies. I should really do it with discrete logic and amps, but hey, it's a quickie. Now, one of my projects is to do with making a multi-channel drone synthesizer. So, been playing with my STM8S-discovery boards, here's some stuff you might like.

Stm8 cosmic pwm example