raspberrypi : Check UART before claiming pins, claim it after

Co-authored-by: Scott Shawcroft <[email protected]>

Author: arturo182

ports/raspberrypi/common-hal/busio/UART.c

@@ -118,16 +118,16 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
 
     uint8_t uart_id = ((((tx != NULL) ? tx->number : rx->number) + 4) / 8) % NUM_UARTS;
 
+    if (uart_status[uart_id] != STATUS_FREE) {
+        mp_raise_RuntimeError(translate("All UART peripherals are in use"));
+    }
+    // These may raise exceptions if pins are already in use.
     self->tx_pin = pin_init(uart_id, tx, 0);
     self->rx_pin = pin_init(uart_id, rx, 1);
     self->cts_pin = pin_init(uart_id, cts, 2);
     self->rts_pin = pin_init(uart_id, rts, 3);
+    uart_status[uart_id] = STATUS_BUSY;
 
-    if (uart_status[uart_id] != STATUS_FREE) {
-        mp_raise_RuntimeError(translate("All UART peripherals are in use"));
-    } else {
-        uart_status[uart_id] = STATUS_BUSY;
-    }
 
     self->uart = UART_INST(uart_id);
     self->uart_id = uart_id;