Hi,
On 7/9/20 4:50 PM, Andy Shevchenko wrote:
On Wed, Jul 08, 2020 at 11:14:22PM +0200, Hans de Goede wrote:
The datasheet specifies that programming the base_unit part of the
ctrl register to 0 results in a contineous low signal.
Adjust the get_state method to reflect this by setting pwm_state.period
to 1 and duty_cycle to 0.
...
+ if (freq == 0) {
+ /* In this case the PWM outputs a continous low signal */
+ state->period = 1;
I guess this should be something like half of the range (so base unit calc
will give 128). Because with period = 1 (too small) it will give too small
base unit (if apply) and as a result we get high frequency pulses.
You are right, that if after this the user only changes the duty-cycle
things will work very poorly, we will end up with a base_unit value of
e.g 65535 and then have almost no duty-cycle resolution at all.
How about using a value here which results in a base_unit value of
256 (for 16 bit base-unit registers), that is the highest frequency we
can do while still having full duty-cycle resolution and it also
is the power-on-reset value, so using a higher period which translates
to a base_unit value of 256 (the por calue) seems like a sensible thing to do.
Uwe what do you think about this?
Regards,
Hans
+ state->duty_cycle = 0;
+ } else {
state->period = NSEC_PER_SEC / (unsigned long)freq;
+ on_time_div *= state->period;
+ do_div(on_time_div, 255);
+ state->duty_cycle = on_time_div;
+ }
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