From 51a62d5387455b328a545febeaf4ea12068209b6 Mon Sep 17 00:00:00 2001
From: Justin Beaurivage <justin@wearableavionics.com>
Date: Tue, 12 Dec 2023 19:27:57 -0500
Subject: [PATCH] Fix nasty bug in I2C-DMA transactions

---
 hal/src/sercom/i2c/async_api.rs | 8 +++++++-
 hal/src/sercom/i2c/flags.rs     | 4 ++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/hal/src/sercom/i2c/async_api.rs b/hal/src/sercom/i2c/async_api.rs
index 4c0548e7f448..c3a23c8d6d83 100644
--- a/hal/src/sercom/i2c/async_api.rs
+++ b/hal/src/sercom/i2c/async_api.rs
@@ -363,6 +363,13 @@ mod dma {
                 .await
                 .map_err(i2c::Error::Dma)?;
 
+            // Unfortunately, gotta take a polling approach here as there is no interrupt
+            // source that can notify us of an IDLE bus state. Fortunately, it's usually not
+            // long. 8-10 times around the loop will do the trick.
+            while !self.i2c.read_status().is_idle() {
+                core::hint::spin_loop();
+            }
+            self.i2c.read_status().check_bus_error()?;
             Ok(())
         }
 
@@ -397,7 +404,6 @@ mod dma {
             read_buf: &mut [u8],
         ) -> Result<(), i2c::Error> {
             self.write(addr, write_buf).await?;
-            // TODO may need some sort of delay here??
             self.read(addr, read_buf).await?;
             Ok(())
         }
diff --git a/hal/src/sercom/i2c/flags.rs b/hal/src/sercom/i2c/flags.rs
index 9731424e6755..a5a3620d068f 100644
--- a/hal/src/sercom/i2c/flags.rs
+++ b/hal/src/sercom/i2c/flags.rs
@@ -70,6 +70,10 @@ impl Status {
             Ok(())
         }
     }
+
+    pub fn is_idle(self) -> bool {
+        self.busstate() == BusState::Idle
+    }
 }
 
 /// Errors available for I2C transactions