adafruit · tannewt · Apr 15, 2025 · Apr 7, 2025 · Apr 8, 2025 · Apr 8, 2025
diff --git a/ports/raspberrypi/mpconfigport.h b/ports/raspberrypi/mpconfigport.h
@@ -33,6 +33,11 @@
 
 #define CIRCUITPY_PROCESSOR_COUNT           (2)
 
+// For many RP2 boards BOOTSEL is not connected to a GPIO pin.
+#ifndef CIRCUITPY_BOOT_BUTTON
+#define CIRCUITPY_BOOT_BUTTON_NO_GPIO       (1)
+#endif
+
 #if CIRCUITPY_USB_HOST
 #define CIRCUITPY_USB_HOST_INSTANCE 1
 #endif

diff --git a/ports/raspberrypi/supervisor/port.c b/ports/raspberrypi/supervisor/port.c
@@ -56,6 +56,13 @@
 #include "RP2350.h" // CMSIS
 #endif
 
+#if CIRCUITPY_BOOT_BUTTON_NO_GPIO
+#include "hardware/gpio.h"
+#include "hardware/sync.h"
+#include "hardware/structs/ioqspi.h"
+#include "hardware/structs/sio.h"
+#endif
+
 #include "supervisor/shared/serial.h"
 
 #include "tusb.h"
@@ -576,3 +583,53 @@ void port_boot_info(void) {
     mp_printf(&mp_plat_print, "\n");
     #endif
 }
+
+#if CIRCUITPY_BOOT_BUTTON_NO_GPIO
+bool __no_inline_not_in_flash_func(port_boot_button_pressed)(void) {
+    // Sense the state of the boot button. Because this function
+    // disables flash, it cannot be safely called once the second
+    // core has been started. When the BOOTSEL button is sensed as
+    // pressed, return is delayed until the button is released and
+    // a delay has passed in order to debounce the button.
+    const uint32_t CS_PIN_INDEX = 1;
+    #if defined(PICO_RP2040)
+    const uint32_t CS_BIT = 1u << 1;
+    #else
+    const uint32_t CS_BIT = SIO_GPIO_HI_IN_QSPI_CSN_BITS;
+    #endif
+    uint32_t int_state = save_and_disable_interrupts();
+    // Wait for any outstanding XIP activity to finish. Flash
+    // must be quiescent before disabling the chip select. Since
+    // there's no XIP busy indication we can test, we delay a
+    // generous 5 ms to allow any XIP activity to finish.
+    busy_wait_us(5000);
+    // Float the flash chip select pin. The line will HI-Z due to
+    // the external 10K pull-up resistor.
+    hw_write_masked(&ioqspi_hw->io[CS_PIN_INDEX].ctrl,
+        GPIO_OVERRIDE_LOW << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
+            IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);
+    // Delay 100 us to allow the CS line to stabilize. If BOOTSEL is
+    // pressed, the line will be pulled low by the button and its
+    // 1K external resistor to ground.
+    busy_wait_us(100);
+    bool button_pressed = !(sio_hw->gpio_hi_in & CS_BIT);
+    // Wait for the button to be released.
+    if (button_pressed) {
+        while (!(sio_hw->gpio_hi_in & CS_BIT)) {
+            tight_loop_contents();
+        }
+        // Wait for 50 ms to debounce the button.
+        busy_wait_us(50000);
+    }
+    // Restore the flash chip select pin to its original state.
+    hw_write_masked(&ioqspi_hw->io[CS_PIN_INDEX].ctrl,
+        GPIO_OVERRIDE_NORMAL << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
+            IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);
+    // Delay 5 ms to allow the flash chip to re-enable and for the
+    // flash CS pin to stabilize.
+    busy_wait_us(5000);
+    // Restore the interrupt state.
+    restore_interrupts(int_state);
+    return button_pressed;
+}
+#endif
diff --git a/py/circuitpy_mpconfig.h b/py/circuitpy_mpconfig.h
@@ -635,6 +635,15 @@ void background_callback_run_all(void);
 #define CIRCUITPY_SAVES_PARTITION_SIZE 0
 #endif
 
+// Boards that have a boot button connected to a GPIO pin should set
+// CIRCUITPY_BOOT_BUTTON_NO_GPIO to 1.
+#ifndef CIRCUITPY_BOOT_BUTTON_NO_GPIO
+#define CIRCUITPY_BOOT_BUTTON_NO_GPIO (0)
+#endif
+#if defined(CIRCUITPY_BOOT_BUTTON) && CIRCUITPY_BOOT_BUTTON_NO_GPIO
+#error "CIRCUITPY_BOOT_BUTTON and CIRCUITPY_BOOT_BUTTON_NO_GPIO are mutually exclusive"
+#endif
+
 #if defined(__GNUC__) && !defined(__ZEPHYR__)
 #if __GNUC__ < CIRCUITPY_MIN_GCC_VERSION
 // (the 3 level scheme here is required to get expansion & stringization

diff --git a/supervisor/port.h b/supervisor/port.h
@@ -108,3 +108,8 @@ void port_boot_info(void);
 // Some ports want to mark additional pointers as gc roots.
 // A default weak implementation is provided that does nothing.
 void port_gc_collect(void);
+
+// Most ports that implement CIRCUITPY_BOOT_BUTTON use a generic version of
+// this function to sense the button. Ports that need to can override this
+// function to provide their own implementation.
+bool port_boot_button_pressed(void);
diff --git a/supervisor/shared/bluetooth/bluetooth.c b/supervisor/shared/bluetooth/bluetooth.c
@@ -10,16 +10,13 @@
 
 #include "shared-bindings/_bleio/__init__.h"
 #include "shared-bindings/_bleio/Adapter.h"
-#if defined(CIRCUITPY_BOOT_BUTTON)
-#include "shared-bindings/digitalio/DigitalInOut.h"
-#include "shared-bindings/time/__init__.h"
-#endif
 #include "shared-bindings/microcontroller/Processor.h"
 #include "shared-bindings/microcontroller/ResetReason.h"
 #include "shared-module/storage/__init__.h"
 
 #include "common-hal/_bleio/__init__.h"
 
+#include "supervisor/port.h"
 #include "supervisor/shared/serial.h"
 #include "supervisor/shared/status_leds.h"
 #include "supervisor/shared/tick.h"
@@ -238,18 +235,10 @@ void supervisor_bluetooth_init(void) {
             new_status_color(BLACK);
         }
         #endif
-        // Init the boot button every time in case it is used for LEDs.
-        #ifdef CIRCUITPY_BOOT_BUTTON
-        digitalio_digitalinout_obj_t boot_button;
-        common_hal_digitalio_digitalinout_construct(&boot_button, CIRCUITPY_BOOT_BUTTON);
-        common_hal_digitalio_digitalinout_switch_to_input(&boot_button, PULL_UP);
-        common_hal_time_delay_ms(1);
-        bool button_pressed = !common_hal_digitalio_digitalinout_get_value(&boot_button);
-        common_hal_digitalio_digitalinout_deinit(&boot_button);
-        if (button_pressed) {
+        if (port_boot_button_pressed()) {
             boot_in_discovery_mode = true;
+            break;
         }
-        #endif
         diff = supervisor_ticks_ms64() - start_ticks;
     }
     if (boot_in_discovery_mode) {

diff --git a/supervisor/shared/port.c b/supervisor/shared/port.c
@@ -12,6 +12,11 @@
 
 #include "lib/tlsf/tlsf.h"
 
+#ifdef CIRCUITPY_BOOT_BUTTON
+#include "shared-bindings/digitalio/DigitalInOut.h"
+#include "shared-bindings/time/__init__.h"
+#endif
+
 static tlsf_t heap;
 
 MP_WEAK void port_wake_main_task(void) {
@@ -60,3 +65,18 @@ MP_WEAK size_t port_heap_get_largest_free_size(void) {
     // IDF does this. Not sure why.
     return tlsf_fit_size(heap, max_size);
 }
+
+MP_WEAK bool port_boot_button_pressed(void) {
+    #if defined(CIRCUITPY_BOOT_BUTTON)
+    // Init/deinit the boot button every time in case it is used for LEDs.
+    digitalio_digitalinout_obj_t boot_button;
+    common_hal_digitalio_digitalinout_construct(&boot_button, CIRCUITPY_BOOT_BUTTON);
+    common_hal_digitalio_digitalinout_switch_to_input(&boot_button, PULL_UP);
+    common_hal_time_delay_ms(1);
+    bool button_pressed = !common_hal_digitalio_digitalinout_get_value(&boot_button);
+    common_hal_digitalio_digitalinout_deinit(&boot_button);
+    return button_pressed;
+    #else
+    return false;
+    #endif
+}
diff --git a/supervisor/shared/safe_mode.c b/supervisor/shared/safe_mode.c
@@ -8,10 +8,6 @@
 
 #include "mphalport.h"
 
-#if defined(CIRCUITPY_BOOT_BUTTON)
-#include "shared-bindings/digitalio/DigitalInOut.h"
-#include "shared-bindings/time/__init__.h"
-#endif
 #include "shared-bindings/microcontroller/Processor.h"
 #include "shared-bindings/microcontroller/ResetReason.h"
 
@@ -78,19 +74,10 @@ safe_mode_t wait_for_safe_mode_reset(void) {
             new_status_color(BLACK);
         }
         #endif
-        // Init the boot button every time in case it is used for LEDs.
-        #ifdef CIRCUITPY_BOOT_BUTTON
-        digitalio_digitalinout_obj_t boot_button;
-        common_hal_digitalio_digitalinout_construct(&boot_button, CIRCUITPY_BOOT_BUTTON);
-        common_hal_digitalio_digitalinout_switch_to_input(&boot_button, PULL_UP);
-        common_hal_time_delay_ms(1);
-        bool button_pressed = !common_hal_digitalio_digitalinout_get_value(&boot_button);
-        common_hal_digitalio_digitalinout_deinit(&boot_button);
-        if (button_pressed) {
+        if (port_boot_button_pressed()) {
             boot_in_safe_mode = true;
             break;
         }
-        #endif
         diff = supervisor_ticks_ms64() - start_ticks;
     }
     #if CIRCUITPY_STATUS_LED
@@ -142,7 +129,7 @@ void print_safe_mode_message(safe_mode_t reason) {
         case SAFE_MODE_USER:
             #if defined(BOARD_USER_SAFE_MODE_ACTION)
             message = BOARD_USER_SAFE_MODE_ACTION;
-            #elif defined(CIRCUITPY_BOOT_BUTTON)
+            #elif defined(CIRCUITPY_BOOT_BUTTON) || CIRCUITPY_BOOT_BUTTON_NO_GPIO
             message = MP_ERROR_TEXT("You pressed the BOOT button at start up");
             #else
             message = MP_ERROR_TEXT("You pressed the reset button during boot.");