Detect lack of pulldown; check for pin in use

shared-bindings/touchio/TouchIn.c

@@ -68,10 +68,11 @@ STATIC mp_obj_t touchio_touchin_make_new(const mp_obj_type_t *type,
     // 1st argument is the pin
     mp_obj_t pin_obj = args[0];
     assert_pin(pin_obj, false);
+    const mcu_pin_obj_t *pin = MP_OBJ_TO_PTR(pin_obj);
+    assert_pin_free(pin);
 
     touchio_touchin_obj_t *self = m_new_obj(touchio_touchin_obj_t);
     self->base.type = &touchio_touchin_type;
-    const mcu_pin_obj_t *pin = MP_OBJ_TO_PTR(pin_obj);
     common_hal_touchio_touchin_construct(self, pin);
 
     return (mp_obj_t) self;

shared-module/touchio/TouchIn.c

@@ -67,12 +67,17 @@ static uint16_t get_raw_reading(touchio_touchin_obj_t *self) {
 }
 
 void common_hal_touchio_touchin_construct(touchio_touchin_obj_t* self, const mcu_pin_obj_t *pin) {
+    claim_pin(pin);
     self->digitalinout = m_new_obj(digitalio_digitalinout_obj_t);
     self->digitalinout->base.type = &digitalio_digitalinout_type;
 
     common_hal_digitalio_digitalinout_construct(self->digitalinout, pin);
 
-    self->threshold = get_raw_reading(self) * 1.05 + 100;
+    uint16_t raw_reading = get_raw_reading(self);
+    if (raw_reading == TIMEOUT_TICKS) {
+        mp_raise_ValueError(translate("No pulldown on pin; 1Mohm recommended"));
+    }
+    self->threshold = raw_reading * 1.05 + 100;
 }
 
 bool common_hal_touchio_touchin_deinited(touchio_touchin_obj_t* self) {