Merge pull request #1468 from rmja/assume-noise-free

Add assume_noise_free to usart configuration

embassy-stm32/src/usart/mod.rs

@@ -120,6 +120,12 @@ pub struct Config {
     /// read will abort, the error reported and cleared
     /// if false, the error is ignored and cleared
     pub detect_previous_overrun: bool,
+
+    /// Set this to true if the line is considered noise free.
+    /// This will increase the receivers tolerance to clock deviations,
+    /// but will effectively disable noise detection.
+    #[cfg(not(usart_v1))]
+    pub assume_noise_free: bool,
 }
 
 impl Default for Config {
@@ -131,6 +137,8 @@ impl Default for Config {
             parity: Parity::ParityNone,
             // historical behavior
             detect_previous_overrun: false,
+            #[cfg(not(usart_v1))]
+            assume_noise_free: false,
         }
     }
 }
@@ -828,11 +836,17 @@ fn configure(r: Regs, config: &Config, pclk_freq: Hertz, kind: Kind, enable_rx:
 
     #[cfg(not(usart_v1))]
     let mut over8 = false;
-    let mut found = false;
+    let mut found = None;
     for &(presc, _presc_val) in &DIVS {
         let denom = (config.baudrate * presc as u32) as u64;
         let div = (pclk_freq.0 as u64 * mul + (denom / 2)) / denom;
-        trace!("USART: presc={} div={:08x}", presc, div);
+        trace!(
+            "USART: presc={}, div=0x{:08x} (mantissa = {}, fraction = {})",
+            presc,
+            div,
+            div >> 4,
+            div & 0x0F
+        );
 
         if div < brr_min {
             #[cfg(not(usart_v1))]
@@ -844,24 +858,36 @@ fn configure(r: Regs, config: &Config, pclk_freq: Hertz, kind: Kind, enable_rx:
                     #[cfg(usart_v4)]
                     r.presc().write(|w| w.set_prescaler(_presc_val));
                 }
-                found = true;
+                found = Some(div);
                 break;
             }
             panic!("USART: baudrate too high");
         }
 
         if div < brr_max {
+            let div = div as u32;
             unsafe {
-                r.brr().write_value(regs::Brr(div as u32));
+                r.brr().write_value(regs::Brr(div));
                 #[cfg(usart_v4)]
                 r.presc().write(|w| w.set_prescaler(_presc_val));
             }
-            found = true;
+            found = Some(div);
             break;
         }
     }
 
-    assert!(found, "USART: baudrate too low");
+    let div = found.expect("USART: baudrate too low");
+
+    #[cfg(not(usart_v1))]
+    let oversampling = if over8 { "8 bit" } else { "16 bit" };
+    #[cfg(usart_v1)]
+    let oversampling = "default";
+    trace!(
+        "Using {} oversampling, desired baudrate: {}, actual baudrate: {}",
+        oversampling,
+        config.baudrate,
+        pclk_freq.0 / div
+    );
 
     unsafe {
         r.cr2().write(|w| {
@@ -895,6 +921,11 @@ fn configure(r: Regs, config: &Config, pclk_freq: Hertz, kind: Kind, enable_rx:
             #[cfg(not(usart_v1))]
             w.set_over8(vals::Over8(over8 as _));
         });
+
+        #[cfg(not(usart_v1))]
+        r.cr3().modify(|w| {
+            w.set_onebit(config.assume_noise_free);
+        });
     }
 }