85 lines
2.4 KiB
Rust
85 lines
2.4 KiB
Rust
//! USART1 transmit configuration for STM32F722.
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use stm32f7::stm32f722;
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/// UART baud-rate configuration error.
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#[derive(Clone, Copy, Debug, Eq, PartialEq)]
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pub enum BaudRateError {
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/// Zero is not a valid baud rate.
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Zero,
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/// The requested divisor cannot fit USART BRR.
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OutOfRange,
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}
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/// Owns configured transmit-only USART1 hardware.
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///
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/// Pin alternate-function setup remains board-owned because it depends on the
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/// schematic. Configure pins before constructing this type.
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pub struct Usart1Tx {
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peripheral: stm32f722::USART1,
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}
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impl Usart1Tx {
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/// Enables USART1 and configures 8N1 transmit-only operation.
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pub fn new(
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rcc: &stm32f722::RCC,
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peripheral: stm32f722::USART1,
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peripheral_clock_hz: u32,
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baud: u32,
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) -> Result<Self, BaudRateError> {
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let brr = calculate_brr(peripheral_clock_hz, baud)?;
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rcc.apb2rstr()
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.modify(|_, write| write.usart1rst().set_bit());
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rcc.apb2rstr()
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.modify(|_, write| write.usart1rst().clear_bit());
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rcc.apb2enr().modify(|_, write| write.usart1en().set_bit());
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peripheral.brr().write(|write| {
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// SAFETY: `brr` is validated to fit the complete BRR register.
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unsafe { write.bits(u32::from(brr)) }
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});
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peripheral
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.cr1()
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.write(|write| write.te().set_bit().ue().set_bit());
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peripheral.cr2().write(|write| write.stop().stop1());
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Ok(Self { peripheral })
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}
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pub(crate) fn enable_dma_transmit(&self) {
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self.peripheral.cr3().write(|write| write.dmat().set_bit());
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}
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pub(crate) fn transmit_data_register_address(&self) -> u32 {
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self.peripheral.tdr().as_ptr() as u32
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}
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}
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const fn calculate_brr(peripheral_clock_hz: u32, baud: u32) -> Result<u16, BaudRateError> {
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if baud == 0 {
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return Err(BaudRateError::Zero);
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}
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let divisor = (peripheral_clock_hz + (baud / 2)) / baud;
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if divisor == 0 || divisor > u16::MAX as u32 {
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Err(BaudRateError::OutOfRange)
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} else {
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Ok(divisor as u16)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::{BaudRateError, calculate_brr};
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#[test]
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fn calculates_reset_clock_brr() {
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assert_eq!(calculate_brr(16_000_000, 115_200), Ok(139));
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}
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#[test]
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fn rejects_zero_baud() {
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assert_eq!(calculate_brr(16_000_000, 0), Err(BaudRateError::Zero));
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}
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}
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