Add ability to read VOLTAGE_MONITOR on Pico W

Because this must be treated like an in-use pin for all other purposes,
unfortunately a special case must be added in shared-bindings.

Multiple AnalogIn objects for VOLTAGE_MONITOR can be created (because
in use tracking isn't working) but this causes no harm.

Testing performed: Read the monitor, then imported wifi. When the
pin state was insufficiently restored, the second step would fail
with debug messages about do_ioctl timeout.

```
import analogio, board
a = analogio.AnalogIn(board.VOLTAGE_MONITOR)
print(a.value)
import wifi
```

Closes: #7020

ports/raspberrypi/bindings/cyw43/__init__.c

@@ -123,6 +123,14 @@ const mcu_pin_obj_t *validate_obj_is_pin_including_cyw43(mp_obj_t obj) {
     return MP_OBJ_TO_PTR(obj);
 }
 
+const mcu_pin_obj_t *validate_obj_is_free_pin_or_gpio29(mp_obj_t obj) {
+    const mcu_pin_obj_t *pin = validate_obj_is_pin(obj);
+    if (obj != &pin_GPIO29) {
+        assert_pin_free(pin);
+    }
+    return pin;
+}
+
 const mcu_pin_obj_t *validate_obj_is_free_pin_including_cyw43(mp_obj_t obj) {
     const mcu_pin_obj_t *pin = validate_obj_is_pin_including_cyw43(obj);
     assert_pin_free(pin);

ports/raspberrypi/bindings/cyw43/__init__.h

@@ -32,6 +32,7 @@
 
 extern const mp_obj_type_t cyw43_pin_type;
 const mcu_pin_obj_t *validate_obj_is_free_pin_including_cyw43(mp_obj_t obj);
+const mcu_pin_obj_t *validate_obj_is_free_pin_or_gpio29(mp_obj_t obj);
 const mcu_pin_obj_t *validate_obj_is_pin_including_cyw43(mp_obj_t obj);
 
 #define CONSTANT_CYW43_PM_VALUE(pm_mode, pm2_sleep_ret_ms, li_beacon_period, li_dtim_period, li_assoc) \

ports/raspberrypi/boards/raspberry_pi_pico_w/pins.c

@@ -45,6 +45,10 @@ STATIC const mp_rom_map_elem_t board_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_GP28), MP_ROM_PTR(&pin_GPIO28) },
     { MP_ROM_QSTR(MP_QSTR_A2), MP_ROM_PTR(&pin_GPIO28) },
 
+    { MP_ROM_QSTR(MP_QSTR_VOLTAGE_MONITOR), MP_ROM_PTR(&pin_GPIO29) },
+    { MP_ROM_QSTR(MP_QSTR_A3), MP_ROM_PTR(&pin_GPIO29) },
+
+
     { MP_ROM_QSTR(MP_QSTR_STEMMA_I2C), MP_ROM_PTR(&board_i2c_obj) },
 };
 MP_DEFINE_CONST_DICT(board_module_globals, board_module_globals_table);

ports/raspberrypi/common-hal/analogio/AnalogIn.c

@@ -35,16 +35,26 @@
 #define ADC_FIRST_PIN_NUMBER 26
 #define ADC_PIN_COUNT 4
 
+// Voltage monitor is special on Pico W, because this pin is shared between the
+// voltage monitor function and the wifi function. Special handling is required
+// to read the analog voltage.
+#if CIRCUITPY_CYW43
+#define SPECIAL_PIN(pin) (pin->number == 29)
+#else
+#define SPECIAL_PIN(pin) false
+#endif
+
 void common_hal_analogio_analogin_construct(analogio_analogin_obj_t *self, const mcu_pin_obj_t *pin) {
     if (pin->number < ADC_FIRST_PIN_NUMBER || pin->number > ADC_FIRST_PIN_NUMBER + ADC_PIN_COUNT) {
         raise_ValueError_invalid_pin();
     }
 
     adc_init();
+    if (!SPECIAL_PIN(pin)) {
+        adc_gpio_init(pin->number);
+        claim_pin(pin);
+    }
 
-    adc_gpio_init(pin->number);
-
-    claim_pin(pin);
     self->pin = pin;
 }
 
@@ -57,14 +67,29 @@ void common_hal_analogio_analogin_deinit(analogio_analogin_obj_t *self) {
         return;
     }
 
-    reset_pin_number(self->pin->number);
+    if (!SPECIAL_PIN(self->pin)) {
+        reset_pin_number(self->pin->number);
+    }
     self->pin = NULL;
 }
 
 uint16_t common_hal_analogio_analogin_get_value(analogio_analogin_obj_t *self) {
-    adc_select_input(self->pin->number - ADC_FIRST_PIN_NUMBER);
-    uint16_t value = adc_read();
-
+    uint16_t value;
+    if (SPECIAL_PIN(self->pin)) {
+        common_hal_mcu_disable_interrupts();
+        uint32_t old_pad = padsbank0_hw->io[self->pin->number];
+        uint32_t old_ctrl = iobank0_hw->io[self->pin->number].ctrl;
+        adc_gpio_init(self->pin->number);
+        adc_select_input(self->pin->number - ADC_FIRST_PIN_NUMBER);
+        value = adc_read();
+        gpio_init(self->pin->number);
+        padsbank0_hw->io[self->pin->number] = old_pad;
+        iobank0_hw->io[self->pin->number].ctrl = old_ctrl;
+        common_hal_mcu_enable_interrupts();
+    } else {
+        adc_select_input(self->pin->number - ADC_FIRST_PIN_NUMBER);
+        value = adc_read();
+    }
     // Stretch 12-bit ADC reading to 16-bit range
     return (value << 4) | (value >> 8);
 }

shared-bindings/analogio/AnalogIn.c

@@ -36,6 +36,10 @@
 #include "shared-bindings/analogio/AnalogIn.h"
 #include "shared-bindings/util.h"
 
+#if CIRCUITPY_CYW43
+#include "bindings/cyw43/__init__.h"
+#endif
+
 //| class AnalogIn:
 //|     """Read analog voltage levels
 //|
@@ -60,8 +64,11 @@ STATIC mp_obj_t analogio_analogin_make_new(const mp_obj_type_t *type,
     mp_arg_check_num(n_args, n_kw, 1, 1, false);
 
     // 1st argument is the pin
+    #if CIRCUITPY_CYW43
+    const mcu_pin_obj_t *pin = validate_obj_is_free_pin_or_gpio29(args[0]);
+    #else
     const mcu_pin_obj_t *pin = validate_obj_is_free_pin(args[0]);
-
+    #endif
     analogio_analogin_obj_t *self = m_new_obj(analogio_analogin_obj_t);
     self->base.type = &analogio_analogin_type;
     common_hal_analogio_analogin_construct(self, pin);