generic: i2c: Fix ping_device hanging in read mode

It turns out that I2C by design cannot perform zero-sized read
transfers.  After the bus master addresses a peripheral in read-mode,
the peripheral acknowledges and **immediately** sends the first byte of
data before the bus master can interrupt again.

Thus, the previous implementation of probing devices and immediately
sending a stop after they acknowledge leads to an illegal bus situation.
Instead, we must wait for the first byte to be clocked out and only then
interrupt further transmission with a NACK.

Link: #622 (comment)

Author: bdew

avr-hal-generic/src/i2c.rs

@@ -289,6 +289,9 @@ where
     pub fn ping_device(&mut self, address: u8, direction: Direction) -> Result<bool, Error> {
         match self.p.raw_start(address, direction) {
             Ok(_) => {
+                if direction == Direction::Read {
+                    self.p.raw_read(&mut [0], true)?
+                }
                 self.p.raw_stop()?;
                 Ok(true)
             }