Fix loop condition

Author: bugadani

esp-hal/CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - RMT: `ChannelCreator::configure_tx` and `ChannelCreator::configure_rx` don't take a pin anymore, instead `Channel::with_pin` has been added. (#4302)
 - RMT: Configuration errors have been split out of `rmt::Error` into the new `rmt::ConfigError` enum. (#4494)
 - RMT: `Rmt::new()` now returns `Error::UnreachableTargetFrequency` instead of panicking when requesting 0 Hz. (#4509)
+- UART: changed the FIFO threshold in `read_exact_async` to reduce the likelyhood of `FifoOverflowed` errors. (#?)
 
 - Internal clock configuration rework (#4501)
 

esp-hal/src/uart/mod.rs

@@ -1072,23 +1072,28 @@ impl<'d> UartRx<'d, Async> {
     async fn wait_for_buffered_data(
         &mut self,
         minimum: usize,
-        preferred: usize,
+        max_threshold: usize,
         listen_for_timeout: bool,
     ) -> Result<(), RxError> {
-        while self.uart.info().rx_fifo_count() < (minimum as u16).min(Info::RX_FIFO_MAX_THRHD) {
-            let amount = u16::try_from(preferred)
-                .unwrap_or(Info::RX_FIFO_MAX_THRHD)
-                .min(Info::RX_FIFO_MAX_THRHD);
+        let current_threshold = self.uart.info().rx_fifo_full_threshold();
 
-            let current = self.uart.info().rx_fifo_full_threshold();
-            let _guard = if current > amount {
+        // User preference takes priority.
+        let max_threshold = max_threshold.min(current_threshold as usize) as u16;
+        let minimum = minimum.min(Info::RX_FIFO_MAX_THRHD as usize) as u16;
+
+        // The effective threshold must be >= minimum. We ensure this by lowering the minimum number
+        // of returnable bytes.
+        let minimum = minimum.min(max_threshold);
+
+        while self.uart.info().rx_fifo_count() < minimum {
+            let _guard = if current_threshold > max_threshold {
                 // We're ignoring the user configuration here to ensure that this is not waiting
                 // for more data than the buffer. We'll restore the original value after the
                 // future resolved.
                 let info = self.uart.info();
-                unwrap!(info.set_rx_fifo_full_threshold(amount));
+                unwrap!(info.set_rx_fifo_full_threshold(max_threshold));
                 Some(OnDrop::new(|| {
-                    unwrap!(info.set_rx_fifo_full_threshold(current));
+                    unwrap!(info.set_rx_fifo_full_threshold(current_threshold));
                 }))
             } else {
                 None