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PWM: Set TOP to 0xfffe by default and fix get_max_duty #744

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Dec 28, 2023
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PWM: Set TOP to 0xfffe by default and fix get_max_duty #744

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18 changes: 15 additions & 3 deletions rp2040-hal/src/pwm/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -343,7 +343,7 @@ where
self.regs.write_div_frac(0); // No divisor
self.regs.write_inv_a(false); //Don't invert the channel
self.regs.write_inv_b(false); //Don't invert the channel
self.regs.write_top(0xffff); // Wrap at max
self.regs.write_top(0xfffe); // Wrap at 0xfffe, so cc = 0xffff can indicate 100% duty cycle
self.regs.write_ctr(0x0000); //Reset the counter
self.regs.write_cc_a(0); //Default duty cycle of 0%
self.regs.write_cc_b(0); //Default duty cycle of 0%
Expand Down Expand Up @@ -420,6 +420,18 @@ where
}

/// Sets the top register value
///
/// Don't set this to 0xffff if you need true 100% duty cycle:
///
/// The CC register, which is used to configure the duty cycle,
/// must be set to TOP + 1 for 100% duty cycle, but also is a
/// 16 bit register.
///
/// In case you do set TOP to 0xffff, [`SetDutyCycle::set_duty_cycle`]
/// will slightly violate the trait's documentation, as
/// `SetDutyCycle::set_duty_cycle_fully_on` and other calls that
/// should lead to 100% duty cycle will only reach a duty cycle of
/// about 99.998%.
#[inline]
pub fn set_top(&mut self, value: u16) {
self.regs.write_top(value)
Expand Down Expand Up @@ -702,7 +714,7 @@ impl<S: AnySlice> PwmPin for Channel<S, B> {
}

fn get_max_duty(&self) -> Self::Duty {
self.regs.read_top()
self.regs.read_top().saturating_add(1)
}

fn set_duty(&mut self, duty: Self::Duty) {
Expand Down Expand Up @@ -845,7 +857,7 @@ pub struct SliceDmaWriteCc<S: SliceId, M: ValidSliceMode<S>> {
/// pwm.channel_b.set_duty(0x1000);
///
/// let buf = singleton!(: [TopFormat; 4] = [TopFormat::new(0x7fff); 4]).unwrap();
/// let buf2 = singleton!(: [TopFormat; 4] = [TopFormat::new(0xffff); 4]).unwrap();
/// let buf2 = singleton!(: [TopFormat; 4] = [TopFormat::new(0xfffe); 4]).unwrap();
///
/// let dma = pac.DMA.split(&mut pac.RESETS);
///
Expand Down
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