Fix SpiBus for use with Polarity::IdleHigh

Instead of just storing the correct polarity, also set this polarity in
the GPIO struct, so that changes that write to GPIOs (e.g. asserting CS)
will maintain the correct idle level.

If this is not done, the FTDI will create invalid output with clock
spikes.

Fixes #75

Author: andreasWallner

src/spi.rs

@@ -118,14 +118,28 @@ where
     /// let device = libftd2xx::Ft2232h::with_description("Dual RS232-HS A")?;
     /// let hal = hal::FtHal::init_freq(device, 3_000_000)?;
     /// let mut spi = hal.spi()?;
-    /// spi.set_clock_polarity(Polarity::IdleLow);
+    /// spi.set_clock_polarity(Polarity::IdleLow)?;
     /// # }
     /// # Ok::<(), std::boxed::Box<dyn std::error::Error>>(())
     /// ```
     ///
     /// [SPI mode]: https://en.wikipedia.org/wiki/Serial_Peripheral_Interface#Mode_numbers
-    pub fn set_clock_polarity<P: Into<Polarity>>(&mut self, cpol: P) {
-        self.pol = cpol.into()
+    pub fn set_clock_polarity<P: Into<Polarity>>(&mut self, cpol: P) -> Result<(), Error<E>> {
+        self.pol = cpol.into();
+        let mut lock = self.mtx.lock().unwrap();
+        match self.pol.clk {
+            ClockData::MsbNegIn | ClockData::LsbNegIn => {
+                lock.lower.value |= 1;
+            }
+            ClockData::MsbPosIn | ClockData::LsbPosIn => {
+                lock.lower.value &= !1;
+            }
+        }
+        let cmd: MpsseCmdBuilder = MpsseCmdBuilder::new()
+            .set_gpio_lower(lock.value, lock.direction)
+            .send_immediate();
+        lock.ft.send(cmd.as_slice())?;
+        Ok(())
     }
 }