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fix: BufferedUartRx embedded_hal_nb::serial::Read impl #3915

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merged 3 commits into from
Feb 24, 2025
Merged

fix: BufferedUartRx embedded_hal_nb::serial::Read impl #3915

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76756ee
fix: BufferedUartRx embedded_hal_nb::serial::Read impl
Feb 24, 2025
c52f567
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Feb 24, 2025
519bd86
fix: Check buffer full before pop_done()
Feb 24, 2025
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29 changes: 10 additions & 19 deletions embassy-stm32/src/usart/buffered.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -908,26 +908,17 @@ impl<'d> embedded_hal_02::serial::Read<u8> for BufferedUartRx<'d> {
type Error = Error;

fn read(&mut self) -> Result<u8, nb::Error<Self::Error>> {
let r = self.info.regs;
unsafe {
let sr = sr(r).read();
if sr.pe() {
rdr(r).read_volatile();
Err(nb::Error::Other(Error::Parity))
} else if sr.fe() {
rdr(r).read_volatile();
Err(nb::Error::Other(Error::Framing))
} else if sr.ne() {
rdr(r).read_volatile();
Err(nb::Error::Other(Error::Noise))
} else if sr.ore() {
rdr(r).read_volatile();
Err(nb::Error::Other(Error::Overrun))
} else if sr.rxne() {
Ok(rdr(r).read_volatile())
} else {
Err(nb::Error::WouldBlock)
let state = self.state;
let mut rx_reader = unsafe { state.rx_buf.reader() };

let do_pend = state.rx_buf.is_full();
if let Some(data) = rx_reader.pop_one() {
if do_pend {
self.info.interrupt.pend();
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why pend if full? this would create an interrupt storm.

it should be the other way: in the Ok branch, if the ringbuffer was full and thanks to this read it stops being full we have to pend the irq to kickstart reading bytes again.

embassy/embassy-stm32/src/usart/buffered.rs

Lines 617 to 621 in c52f567

let full = state.rx_buf.is_full();
rx_reader.pop_done(amt);
if full {
self.info.interrupt.pend();
}

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Yes you are right, I fixed it. The rx_buf full check is done before marking the byte as read.

}
Ok(data)
} else {
Err(nb::Error::WouldBlock)
}
}
}
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