A better fix and Change log update.

CHANGELOG.md

@@ -11,8 +11,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
  - move gpio, dma impls, adc pins in subdir, remove unused `From` impls [#658] [#664]
  - Bump `embedded-hal` to `1.0.0-alpha.10`. See [their changelog][embedded-hal-1.0.0-alpha.10] for further details. Note that this included breaking changes to the previous alpha APIs. [#663]
+ - Fix race condition in sending start condition in I2C. [#662]
 
 [#658]: https://github.com/stm32-rs/stm32f4xx-hal/pull/658
+[#662]: https://github.com/stm32-rs/stm32f4xx-hal/pull/662
 [#663]: https://github.com/stm32-rs/stm32f4xx-hal/pull/663
 [#664]: https://github.com/stm32-rs/stm32f4xx-hal/pull/664
 [embedded-hal-1.0.0-alpha.10]: https://github.com/rust-embedded/embedded-hal/blob/v1.0.0-alpha.10/embedded-hal/CHANGELOG.md

src/i2c/dma.rs

@@ -421,10 +421,15 @@ where
 
     fn send_start(&mut self, read: bool) -> Result<(), super::Error> {
         let i2c = &self.hal_i2c.i2c;
+
+        // Make sure the ack and start bit is set together in a single
+        // read-modify-write operation to avoid race condition.
+        // See PR: https://github.com/stm32-rs/stm32f4xx-hal/pull/662
         if read {
-            i2c.cr1.modify(|_, w| w.ack().set_bit());
+            i2c.cr1.modify(|_, w| w.ack().set_bit().start().set_bit());
+        } else {
+            i2c.cr1.modify(|_, w| w.start().set_bit());
         }
-        i2c.cr1.modify(|_, w| w.start().set_bit());
 
         // Wait until START condition was generated
         while self