On 30/03/2019 20:29, Martin Blumenstingl wrote: > Hello Uwe, > > On Mon, Mar 25, 2019 at 9:07 PM Uwe Kleine-König > <[email protected]> wrote: > [...] >>>> - Does stopping the PWM (i.e. clearing MISC_{A,B}_EN in the MISC_AB >>>> register) freeze the output, or is the currently running period >>>> completed first? (The latter is the right behaviour.) >>> I don't know, I would have to measure this with a logic analyzer. >> >> In practise you can do this with a multimeter, too. Just do something >> like: >> >> pwm_apply_state({ .enabled = true, .period = 5s, .duty_cycle = 5s, >> .polarity = PWM_POLARITY_NORMAL }); >> pwm_apply_state({ .enabled = false, .period = 5s, .duty_cycle = 5s, >> .polarity = PWM_POLARITY_NORMAL }); >> >> (assuming the PWM supports periods that long). The expectation is that >> the last command takes nearly 5 s to complete and while it waits the >> output is high and on return it's low. If that isn't the case, there is >> a bug somewhere. > the longest supported period (using the 24MHz crystal as input, which > is the slowest input clock and thus gives the longest possible > duration) is 349514407ns (that's approx. 0.35 seconds). my multimeter > isn't fast enough to measure this so I'm using my logic analyzer with > puleseview instead: [0] > > I added the following code to meson_pwm_request: > struct pwm_state enable = { > .enabled = true, > .period = 349514407U, > .duty_cycle = 349514407U, > .polarity = PWM_POLARITY_NORMAL }; > struct pwm_state disable = { > .enabled = false, > .period = 349514407U, > .duty_cycle = 349514407U, > .polarity = PWM_POLARITY_NORMAL }; > pwm_apply_state(pwm, &enable); > pwm_apply_state(pwm, &disable); > > this returns immediately. my logic analyzer doesn't see signal change > (I'm sampling at 1MHz). > > can you please confirm that my test code and measurement procedure is correct? > if it is then my observation is that disabling the PWM does so > immediately, without waiting for the current period to complete
I'm pretty 100,00000000000000% sure the HW doesn't permit waiting for a period to finish. For disable states, we can either play on the period (high period at 0xffff for disable at PWM_POLARITY_INVERSED and high period at 0 for PWM_POLARITY_NORMAL, if the HW behaves correctly) or by adding some pinctrl states switching to GPIO modes and adding the enable output high and output low property. Neil > > > Regards > Martin > > > [0] https://sigrok.org/wiki/Lcsoft_Mini_Board >
