http://kmingk.com/audio-project-on-beagle-bone-black/2013/10/30/testing-limits-of-beaglebone-black-pwm
According to him, 9Mhz for audio "safe" PWM. On Fri, Feb 26, 2016 at 7:26 PM, William Hermans <[email protected]> wrote: > *I don't expect any response to this -- I think by now I'm rambling on* >> * very vague hypothetical conditions...* > > > Well then, this post is a figment of your imagination ;) Anyway, I don't > know much of PWM "theory", but just going by the file system attribute > names. Resolution is adjustable to the nanosecond, as is duty cycle. But at > any rate, a 2Mhz PWM would be fairly high. Especially considering that > *a)* this is a "freebie" on die module, and *b)* PWM functionality > requires no additional interaction from the main processor( but changing > parameters does, which is trivial / expected ). > > Anyway, 1ns high, 1ns low. So whatever 2ns works out to. > > On Fri, Feb 26, 2016 at 7:08 PM, Dennis Lee Bieber <[email protected]> > wrote: > >> On Fri, 26 Feb 2016 14:11:08 -0700, William Hermans >> <[email protected]> declaimed the following: >> >> > the PWM pulse rate should not be effected by any software - Period. >> >Changing rates now perhaps would be. sysfs for instance would be slower >> >than using mmap(), or the PRU's, but I'm not exactly sure that the speed >> of >> >which you can change the pulse rate is all that important. For most use >> >cases . . . As something like the control for DC/DC switching would need >> to >> >change dynamically, and very quickly. >> > >> >Anyway, given this, the maximum frequency of the PWM should be what is >> >listed in the TRM for the hardware module. >> > >> Not the easiest document to read (especially for an old >> programmer of >> number cruncher applications on "mainframes"... I've only gotten into the >> embedded world in the last three years and am struggling to understand the >> systems at work)... >> >> But... If I understand that TI document. 100MHz clock. The duty >> cycle >> is a value in a comparison against another value (a counter setting the >> period/wavelength)... So for the minimum square wave, if the duty cycle >> value is "1", the counter limit would need to be "2"... Giving a 50MHz >> square wave (ignoring rise-time slew on the actual output signals -- I >> suspect the output will look more like a triangle wave at that speed). No >> proportional control available. >> >> The section on the "high resolution PWM" shows a table that goes >> all >> the way up to... 2MHz... Though if loss of "1 bit" of HRPWM is equivalent >> to a doubling in frequency, and 2MHz is 11 bits... >> 4 10 >> 8 9 >> 16 8 >> 32 7 >> 64 6 >> >> Regular PWM is less than 6bits at 2MHz and that gives >> 4 5 >> 8 4 >> 16 3 >> 32 2 >> 64 1 bit? >> >> Though reading further indicates that HRPWM works by fine-tuning >> the >> transition point of the regular PWM... So I suspect for a square wave one >> is still limited to the regular PWM rate... and 32MHz might be the >> effective limit. >> >> I don't expect any response to this -- I think by now I'm >> rambling on >> very vague hypothetical conditions... >> -- >> Wulfraed Dennis Lee Bieber AF6VN >> [email protected] HTTP://wlfraed.home.netcom.com/ >> >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> For more options, visit https://groups.google.com/d/optout. >> > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
