> > *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.
