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rp/spi: add set_frequency

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This commit is contained in:
Dario Nieuwenhuis 2021-07-12 02:45:59 +02:00
parent 7547c8d8d6
commit 1a4c13cf26
1 changed files with 41 additions and 34 deletions
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75
embassy-rp/src/spi.rs
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@ -33,6 +33,33 @@ pub struct Spi<'d, T: Instance> {
phantom: PhantomData<&'d mut T>,
}
fn div_roundup(a: u32, b: u32) -> u32 {
(a + b - 1) / b
}
fn calc_prescs(freq: u32) -> (u8, u8) {
let clk_peri = crate::clocks::clk_peri_freq();
// final SPI frequency: spi_freq = clk_peri / presc / postdiv
// presc must be in 2..=254, and must be even
// postdiv must be in 1..=256
// divide extra by 2, so we get rid of the "presc must be even" requirement
let ratio = div_roundup(clk_peri, freq * 2);
if ratio > 127 * 256 {
panic!("Requested too low SPI frequency");
}
let presc = div_roundup(ratio, 256);
let postdiv = if presc == 1 {
ratio
} else {
div_roundup(ratio, presc)
};
((presc * 2) as u8, (postdiv - 1) as u8)
}
impl<'d, T: Instance> Spi<'d, T> {
pub fn new(
inner: impl Unborrow<Target = T>,
@ -46,45 +73,14 @@ impl<'d, T: Instance> Spi<'d, T> {
unsafe {
let p = inner.regs();
let (presc, postdiv) = calc_prescs(config.frequency);
let clk_peri = crate::clocks::clk_peri_freq();
assert!(config.frequency <= clk_peri);
// final SPI frequency: spi_freq = clk_peri / presc / postdiv
// presc must be in 2..=254, and must be even
// postdiv must be in 1..=256
fn div_roundup(a: u32, b: u32) -> u32 {
(a + b - 1) / b
}
// divide extra by 2, so we get rid of the "presc must be even" requirement
let ratio = div_roundup(clk_peri, config.frequency * 2);
if ratio > 127 * 256 {
panic!("Requested too low SPI frequency");
}
let presc = div_roundup(ratio, 256);
let postdiv = if presc == 1 {
ratio
} else {
div_roundup(ratio, presc)
};
debug!(
"SPI: requested freq {=u32}, actual freq {=u32}, presc {=u32}, postdiv {=u32}",
config.frequency,
clk_peri / (presc * 2 * postdiv),
presc * 2,
postdiv
);
p.cpsr().write(|w| w.set_cpsdvsr((presc * 2) as _));
p.cpsr().write(|w| w.set_cpsdvsr(presc));
p.cr0().write(|w| {
w.set_dss(0b0111); // 8bit
w.set_spo(config.polarity == ehnb::Polarity::IdleHigh);
w.set_sph(config.phase == ehnb::Phase::CaptureOnSecondTransition);
w.set_scr((postdiv - 1) as u8);
w.set_scr(postdiv);
});
p.cr1().write(|w| {
w.set_sse(true); // enable
@ -139,6 +135,17 @@ impl<'d, T: Instance> Spi<'d, T> {
while p.sr().read().bsy() {}
}
}
pub fn set_frequency(&mut self, freq: u32) {
let (presc, postdiv) = calc_prescs(freq);
let p = self.inner.regs();
unsafe {
p.cpsr().write(|w| w.set_cpsdvsr(presc));
p.cr0().modify(|w| {
w.set_scr(postdiv);
});
}
}
}
impl<'d, T: Instance> eh::Write<u8> for Spi<'d, T> {