machine/rp2040: implement UART0/UART1, can be used on all rp2040 boards

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/machine/uart.go

@@ -1,4 +1,4 @@
-// +build atmega esp nrf sam sifive stm32 k210 nxp
+// +build atmega esp nrf sam sifive stm32 k210 nxp rp2040
 
 package machine
 
@@ -6,6 +6,23 @@ import "errors"
 
 var errUARTBufferEmpty = errors.New("UART buffer empty")
 
+// UARTParity is the parity setting to be used for UART communication.
+type UARTParity int
+
+const (
+	// ParityNone means to not use any parity checking. This is
+	// the most common setting.
+	ParityNone UARTParity = 0
+
+	// ParityEven means to expect that the total number of 1 bits sent
+	// should be an even number.
+	ParityEven UARTParity = 1
+
+	// ParityOdd means to expect that the total number of 1 bits sent
+	// should be an odd number.
+	ParityOdd UARTParity = 2
+)
+
 type UARTConfig struct {
 	BaudRate uint32
 	TX       Pin