Merge #765

765: Implement Output::is_set_low for embassy-rp r=Dirbaio a=danbev

This commit implements a suggestion for the method `is_set_low` which is
currently a `todo`, by reading last value written to `GPIO_OUT`.

Co-authored-by: Daniel Bevenius <daniel.bevenius@gmail.com>

embassy-rp/src/gpio.rs

@@ -127,8 +127,9 @@ impl<'d, T: Pin> Output<'d, T> {
 
     /// Is the output pin set as low?
     pub fn is_set_low(&self) -> bool {
-        // todo
-        true
+        // Reading from SIO: GPIO_OUT gives the last value written.
+        let val = 1 << self.pin.pin();
+        unsafe { (self.pin.sio_out().value().read() & val) == 0 }
     }
 }