ddr: improve dci divisors calculation
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@ -56,14 +56,35 @@ impl DdrRam {
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clocks
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}
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fn calculate_dci_divisors(clocks: &Clocks) -> (u8, u8) {
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let target = (DCI_FREQ - 1 + clocks.ddr) / DCI_FREQ;
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let mut best = None;
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let mut best_error = 0;
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for divisor0 in 1..63 {
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for divisor1 in 1..63 {
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let current = (divisor0 as u32) * (divisor1 as u32);
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let error = if current > target {
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current - target
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} else {
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target - current
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};
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if best.is_none() || best_error > error {
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best = Some((divisor0, divisor1));
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best_error = error;
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}
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}
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}
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best.unwrap()
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}
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/// Zynq-7000 AP SoC Technical Reference Manual:
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/// 10.6.2 DDR IOB Impedance Calibration
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fn calibrate_iob_impedance(clocks: &Clocks) {
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let divisor0 = ((DCI_FREQ - 1 + clocks.ddr) / DCI_FREQ)
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.max(1).min(63) as u8;
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let divisor1 = ((DCI_FREQ - 1 + clocks.ddr) / DCI_FREQ / u32::from(divisor0))
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.max(1).min(63) as u8;
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debug!("DDR DCI clock: {} Hz", clocks.ddr / u32::from(divisor0) / u32::from(divisor1));
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let (divisor0, divisor1) = Self::calculate_dci_divisors(clocks);
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debug!("DDR DCI clock: {} Hz (divisors={}*{})",
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clocks.ddr / u32::from(divisor0) / u32::from(divisor1),
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divisor0, divisor1);
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slcr::RegisterBlock::unlocked(|slcr| {
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// Step 1.
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