Hello Paul,
On Tue, Jul 23, 2019 at 04:46:40PM -0400, Paul Cercueil wrote:
> Le lun. 22 juil. 2019 à 15:34, Uwe =?iso-8859-1?q?Kleine-K=F6nig?=
> <u.kleine-koenig@xxxxxxxxxxxxxx> a écrit :
> > On Fri, Jun 07, 2019 at 05:44:07PM +0200, Paul Cercueil wrote:
> > > - is_enabled = jz4740_timer_is_enabled(pwm->hwpwm);
> > > - if (is_enabled)
> > > - jz4740_pwm_disable(chip, pwm);
> > > + jz4740_pwm_disable(chip, pwm);
> >
> > I assume this stops the PWM. Does this complete the currently running
> > period? How does the PWM behave then? (Does it still drive the output?
> > If so, on which level?)
>
> Some PWM channels work in one mode "TCU1" and others work in "TCU2". The
> mode in which channels work depends on the version of the SoC.
>
> When stopped, the pins of TCU1 channels will be driven to the inactive
> level (which depends on the polarity). It is unknown whether or not the
> currently running period is completed. We set a bit to configure for
> "abrupt shutdown", so I expect that it's not, but somebody would need
> to hook up a logic analyzer to see what's the exact behaviour with
> and without that bit.
This might be done even without a logic analyzer. Just do something
like:
pwm_apply_state(pwm, { .enabled = 1, .period = 5s })
pwm_apply_state(pwm, { .enabled = 1, .period = 5s, .duty = 5s })
and if that takes less then 5s the period is not completed.
And note that "abrupt shutdown" is a bug.
> TCU2 channels on the other hand will stop in the middle of a period,
> leaving the pin hanging at whatever level it was before the stop.
> That's the rationale behind the trick in commit 6580fd173070 ("pwm:
> jz4740: Force TCU2 channels to return to their init level").
Strange, but ok.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
