Merge #208

208: Updating I2C to wait for STOP to be sent before returning r=therealprof a=ryan-summers

This PR updates the I2C driver to properly wait for the STOP condition to finish transmitting before returning for i2c write and read.

This is necessary to prevent a race condition on the peripheral. If another transaction is started fast enough (before the STOP condition can be sent), it is possible that the I2C state will be mismanaged.

This fixes #207 

I have tested this on a local hardware setup using a large fan of I2C devices where rapid I2C writes and reads are completed in  a loop as part of a self test

Co-authored-by: Ryan Summers <[email protected]>

Author: bors[bot]

src/i2c.rs

@@ -932,6 +932,9 @@ where
         // Send a STOP condition
         self.i2c.cr1.modify(|_, w| w.stop().set_bit());
 
+        // Wait for STOP condition to transmit.
+        while self.i2c.cr1.read().stop().bit_is_set() {}
+
         // Fallthrough is success
         Ok(())
     }
@@ -965,7 +968,10 @@ where
                 .write(|w| unsafe { w.bits((u32::from(addr) << 1) + 1) });
 
             // Wait until address was sent
-            while self.i2c.sr1.read().addr().bit_is_clear() {}
+            while {
+                self.check_and_clear_error_flags()?;
+                self.i2c.sr1.read().addr().bit_is_clear()
+            } {}
 
             // Clear condition by reading SR2
             self.i2c.sr2.read();
@@ -983,6 +989,9 @@ where
             // Receive last byte
             *last = self.recv_byte()?;
 
+            // Wait for the STOP to be sent.
+            while self.i2c.cr1.read().stop().bit_is_set() {}
+
             // Fallthrough is success
             Ok(())
         } else {