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stm32/usart: Implement data bit selection #3595

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Dec 1, 2024
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stm32/usart: Implement data bit selection #3595

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85 changes: 63 additions & 22 deletions embassy-stm32/src/usart/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,6 +91,8 @@ unsafe fn on_interrupt(r: Regs, s: &'static State) {
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
/// Number of data bits
pub enum DataBits {
/// 7 Data Bits
DataBits7,
/// 8 Data Bits
DataBits8,
/// 9 Data Bits
Expand Down Expand Up @@ -134,6 +136,8 @@ pub enum ConfigError {
BaudrateTooHigh,
/// Rx or Tx not enabled
RxOrTxNotEnabled,
/// Data bits and parity combination not supported
DataParityNotSupported,
}

#[non_exhaustive]
Expand Down Expand Up @@ -1617,39 +1621,76 @@ fn configure(
w.set_re(enable_rx);
}

// configure word size
// if using odd or even parity it must be configured to 9bits
w.set_m0(if config.parity != Parity::ParityNone {
trace!("USART: m0: vals::M0::BIT9");
vals::M0::BIT9
} else {
trace!("USART: m0: vals::M0::BIT8");
vals::M0::BIT8
});
// configure parity
w.set_pce(config.parity != Parity::ParityNone);
w.set_ps(match config.parity {
Parity::ParityOdd => {
trace!("USART: set_ps: vals::Ps::ODD");
vals::Ps::ODD
// configure word size and parity, since the parity bit is inserted into the MSB position,
// it increases the effective word size
match (config.parity, config.data_bits) {
(Parity::ParityNone, DataBits::DataBits8) => {
trace!("USART: m0: 8 data bits, no parity");
w.set_m0(vals::M0::BIT8);
#[cfg(any(usart_v3, usart_v4))]
w.set_m1(vals::M1::M0);
w.set_pce(false);
}
(Parity::ParityNone, DataBits::DataBits9) => {
trace!("USART: m0: 9 data bits, no parity");
w.set_m0(vals::M0::BIT9);
#[cfg(any(usart_v3, usart_v4))]
w.set_m1(vals::M1::M0);
w.set_pce(false);
}
#[cfg(any(usart_v3, usart_v4))]
(Parity::ParityNone, DataBits::DataBits7) => {
trace!("USART: m0: 7 data bits, no parity");
w.set_m0(vals::M0::BIT8);
w.set_m1(vals::M1::BIT7);
w.set_pce(false);
}
(Parity::ParityEven, DataBits::DataBits8) => {
trace!("USART: m0: 8 data bits, even parity");
w.set_m0(vals::M0::BIT9);
#[cfg(any(usart_v3, usart_v4))]
w.set_m1(vals::M1::M0);
w.set_pce(true);
w.set_ps(vals::Ps::EVEN);
}
(Parity::ParityEven, DataBits::DataBits7) => {
trace!("USART: m0: 7 data bits, even parity");
w.set_m0(vals::M0::BIT8);
#[cfg(any(usart_v3, usart_v4))]
w.set_m1(vals::M1::M0);
w.set_pce(true);
w.set_ps(vals::Ps::EVEN);
}
Parity::ParityEven => {
trace!("USART: set_ps: vals::Ps::EVEN");
vals::Ps::EVEN
(Parity::ParityOdd, DataBits::DataBits8) => {
trace!("USART: m0: 8 data bits, odd parity");
w.set_m0(vals::M0::BIT9);
#[cfg(any(usart_v3, usart_v4))]
w.set_m1(vals::M1::M0);
w.set_pce(true);
w.set_ps(vals::Ps::ODD);
}
(Parity::ParityOdd, DataBits::DataBits7) => {
trace!("USART: m0: 7 data bits, odd parity");
w.set_m0(vals::M0::BIT8);
#[cfg(any(usart_v3, usart_v4))]
w.set_m1(vals::M1::M0);
w.set_pce(true);
w.set_ps(vals::Ps::ODD);
}
_ => {
trace!("USART: set_ps: vals::Ps::EVEN");
vals::Ps::EVEN
return Err(ConfigError::DataParityNotSupported);
}
});
}
#[cfg(not(usart_v1))]
w.set_over8(vals::Over8::from_bits(over8 as _));
#[cfg(usart_v4)]
{
trace!("USART: set_fifoen: true (usart_v4)");
w.set_fifoen(true);
}
});

Ok(())
})?;

Ok(())
}
Expand Down