Initial commit

CMakeLists.txt

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+add_library(bootsel_reset INTERFACE)
+
+if (PICO_ON_DEVICE)
+	target_sources(bootsel_reset INTERFACE
+		${CMAKE_CURRENT_LIST_DIR}/bootsel_reset.c
+	)
+
+	target_link_libraries(bootsel_reset INTERFACE
+		pico_bootrom
+		pico_stdlib
+	)
+endif()

bootsel_reset.c

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+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "hardware/gpio.h"
+#include "hardware/sync.h"
+#include "hardware/structs/ioqspi.h"
+#include "hardware/structs/sio.h"
+#include "pico/bootrom.h"
+
+// Allow user override of the LED mask and check time (in ms)
+#ifndef USB_BOOT_LED_ACTIVITY_MASK
+#define USB_BOOT_LED_ACTIVITY_MASK 0
+#endif
+#ifndef BOOTSEL_RESET_PERIOD_MS
+#define BOOTSEL_RESET_PERIOD_MS 100
+#endif
+
+// This function taken from pico-examples/src/picoboard/button/button.c
+// Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+// SPDX-License-Identifier: BSD-3-Clause
+//
+// Picoboard has a button attached to the flash CS pin, which the bootrom
+// checks, and jumps straight to the USB bootcode if the button is pressed
+// (pulling flash CS low). We can check this pin in by jumping to some code in
+// SRAM (so that the XIP interface is not required), floating the flash CS
+// pin, and observing whether it is pulled low.
+//
+// This doesn't work if others are trying to access flash at the same time,
+// e.g. XIP streamer, or the other core.
+
+static bool __no_inline_not_in_flash_func(get_bootsel_button)() {
+	const uint CS_PIN_INDEX = 1;
+
+	// Must disable interrupts, as interrupt handlers may be in flash, and we
+	// are about to temporarily disable flash access!
+	uint32_t flags = save_and_disable_interrupts();
+
+	// Set chip select to Hi-Z
+	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
+	);
+
+	// Note we can't call into any sleep functions in flash right now
+	for (volatile int i = 0; i < 500; ++i);
+
+	// The HI GPIO registers in SIO can observe and control the 6 QSPI pins.
+	// Note the button pulls the pin *low* when pressed.
+	bool button_state = !(sio_hw->gpio_hi_in & (1u << CS_PIN_INDEX));
+
+	// Need to restore the state of chip select, else we are going to have a
+	// bad time when we return to code in flash!
+	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
+	);
+
+	restore_interrupts(flags);
+
+	return button_state;
+}
+
+static bool repeating_timer_callback(struct repeating_timer *t) {
+	if (get_bootsel_button()) {
+		reset_usb_boot(USB_BOOT_LED_ACTIVITY_MASK, 0);
+	}
+	return true;
+}
+
+static struct repeating_timer timer;
+static void __attribute__((constructor)) bootsel_reset() {
+	add_repeating_timer_ms(
+		BOOTSEL_RESET_PERIOD_MS,
+		repeating_timer_callback,
+		NULL,
+		&timer
+	);
+}
+

examples/.gitignore

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+build

examples/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.12)
+
+include(pico_sdk_import.cmake)
+project(examples)
+pico_sdk_init()
+
+add_subdirectory(../ ${CMAKE_CURRENT_BINARY_DIR}/bootsel_reset)
+
+add_executable(blinky_bootsel_reset
+	blinky_bootsel_reset.c
+)
+
+target_link_libraries(blinky_bootsel_reset
+	pico_stdlib
+	bootsel_reset
+)
+
+pico_add_extra_outputs(blinky_bootsel_reset)

examples/blinky_bootsel_reset.c

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+#include "pico/stdlib.h"
+
+// This just blinks the LED, however if bootsel_reset is linked with it, 
+// the bootsel button is automatically checked, and if pressed, the pico
+// resets to boot mode
+int main() {
+	const uint LED_PIN = 25;
+	gpio_init(LED_PIN);
+	gpio_set_dir(LED_PIN, GPIO_OUT);
+
+	while (true) {
+		gpio_put(LED_PIN, 1);
+		sleep_ms(250);
+		gpio_put(LED_PIN, 0);
+		sleep_ms(250);
+	}
+}

examples/pico_sdk_import.cmake

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+# This is a copy of <PICO_SDK_PATH>/external/pico_sdk_import.cmake
+
+# This can be dropped into an external project to help locate this SDK
+# It should be include()ed prior to project()
+
+if (DEFINED ENV{PICO_SDK_PATH} AND (NOT PICO_SDK_PATH))
+    set(PICO_SDK_PATH $ENV{PICO_SDK_PATH})
+    message("Using PICO_SDK_PATH from environment ('${PICO_SDK_PATH}')")
+endif ()
+
+if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT} AND (NOT PICO_SDK_FETCH_FROM_GIT))
+    set(PICO_SDK_FETCH_FROM_GIT $ENV{PICO_SDK_FETCH_FROM_GIT})
+    message("Using PICO_SDK_FETCH_FROM_GIT from environment ('${PICO_SDK_FETCH_FROM_GIT}')")
+endif ()
+
+if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT_PATH} AND (NOT PICO_SDK_FETCH_FROM_GIT_PATH))
+    set(PICO_SDK_FETCH_FROM_GIT_PATH $ENV{PICO_SDK_FETCH_FROM_GIT_PATH})
+    message("Using PICO_SDK_FETCH_FROM_GIT_PATH from environment ('${PICO_SDK_FETCH_FROM_GIT_PATH}')")
+endif ()
+
+set(PICO_SDK_PATH "${PICO_SDK_PATH}" CACHE PATH "Path to the PICO SDK")
+set(PICO_SDK_FETCH_FROM_GIT "${PICO_SDK_FETCH_FROM_GIT}" CACHE BOOL "Set to ON to fetch copy of PICO SDK from git if not otherwise locatable")
+set(PICO_SDK_FETCH_FROM_GIT_PATH "${PICO_SDK_FETCH_FROM_GIT_PATH}" CACHE FILEPATH "location to download SDK")
+
+if (NOT PICO_SDK_PATH)
+    if (PICO_SDK_FETCH_FROM_GIT)
+        include(FetchContent)
+        set(FETCHCONTENT_BASE_DIR_SAVE ${FETCHCONTENT_BASE_DIR})
+        if (PICO_SDK_FETCH_FROM_GIT_PATH)
+            get_filename_component(FETCHCONTENT_BASE_DIR "${PICO_SDK_FETCH_FROM_GIT_PATH}" REALPATH BASE_DIR "${CMAKE_SOURCE_DIR}")
+        endif ()
+        FetchContent_Declare(
+                pico_sdk
+                GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+                GIT_TAG master
+        )
+        if (NOT pico_sdk)
+            message("Downloading PICO SDK")
+            FetchContent_Populate(pico_sdk)
+            set(PICO_SDK_PATH ${pico_sdk_SOURCE_DIR})
+        endif ()
+        set(FETCHCONTENT_BASE_DIR ${FETCHCONTENT_BASE_DIR_SAVE})
+    else ()
+        message(FATAL_ERROR
+                "PICO SDK location was not specified. Please set PICO_SDK_PATH or set PICO_SDK_FETCH_FROM_GIT to on to fetch from git."
+                )
+    endif ()
+endif ()
+
+get_filename_component(PICO_SDK_PATH "${PICO_SDK_PATH}" REALPATH BASE_DIR "${CMAKE_BINARY_DIR}")
+if (NOT EXISTS ${PICO_SDK_PATH})
+    message(FATAL_ERROR "Directory '${PICO_SDK_PATH}' not found")
+endif ()
+
+set(PICO_SDK_INIT_CMAKE_FILE ${PICO_SDK_PATH}/pico_sdk_init.cmake)
+if (NOT EXISTS ${PICO_SDK_INIT_CMAKE_FILE})
+    message(FATAL_ERROR "Directory '${PICO_SDK_PATH}' does not appear to contain the PICO SDK")
+endif ()
+
+set(PICO_SDK_PATH ${PICO_SDK_PATH} CACHE PATH "Path to the PICO SDK" FORCE)
+
+include(${PICO_SDK_INIT_CMAKE_FILE})