Fix: Timing Issues after display_frame

epd1in54 and epd2in9 were both missing a necessary wait_until_idle call at the end of their display_frame function which sometimes caused invalid/ignored commands/inputs afterwards.

src/epd1in54/mod.rs

@@ -217,7 +217,10 @@ where
         self.interface.cmd(spi, Command::MASTER_ACTIVATION)?;
         // MASTER Activation should not be interupted to avoid currption of panel images
         // therefore a terminate command is send
-        self.interface.cmd(spi, Command::NOP)
+        self.interface.cmd(spi, Command::NOP)?;
+
+        self.wait_until_idle();
+        Ok(())
     }
 
     fn clear_frame(&mut self, spi: &mut SPI) -> Result<(), SPI::Error> {

src/epd2in9/mod.rs

@@ -216,7 +216,10 @@ where
         self.interface.cmd(spi, Command::MASTER_ACTIVATION)?;
         // MASTER Activation should not be interupted to avoid currption of panel images
         // therefore a terminate command is send
-        self.interface.cmd(spi, Command::NOP)
+        self.interface.cmd(spi, Command::NOP)?;
+
+        self.wait_until_idle();
+        Ok(())
     }
 
     fn clear_frame(&mut self, spi: &mut SPI) -> Result<(), SPI::Error> {

src/traits.rs

@@ -123,6 +123,8 @@ where
     ) -> Result<(), SPI::Error>;
 
     /// Displays the frame data from SRAM
+    /// 
+    /// This function waits until the device isn`t busy anymore
     fn display_frame(&mut self, spi: &mut SPI) -> Result<(), SPI::Error>;
 
     /// Clears the frame buffer on the EPD with the declared background color