hello_double_tap: use pico_bootsel_via_double_reset from SDK

system/CMakeLists.txt

@@ -1,5 +1,4 @@
 if (NOT PICO_NO_HARDWARE)
-    add_subdirectory(double_tap_usb_boot)
     add_subdirectory(narrow_io_write)
     add_subdirectory(hello_double_tap)
     add_subdirectory(unique_board_id)

system/double_tap_usb_boot/CMakeLists.txt

@@ -1,13 +0,0 @@
-add_library(double_tap_usb_boot INTERFACE)
-
-# inclusion of this library will allow you to double tap reset within 100ms to launch into bootrom USB bootloader
-if (PICO_ON_DEVICE)
-    target_sources(double_tap_usb_boot INTERFACE
-            ${CMAKE_CURRENT_LIST_DIR}/double_tap_usb_boot.c
-            )
-
-    target_link_libraries(double_tap_usb_boot INTERFACE
-            pico_bootrom
-            pico_time
-            )
-endif ()

system/double_tap_usb_boot/double_tap_usb_boot.c

@@ -1,36 +0,0 @@
-#include "pico.h"
-#include "pico/time.h"
-#include "pico/bootrom.h"
-
-// Allow user override of the LED mask
-#ifndef USB_BOOT_LED_ACTIVITY_MASK
-#define USB_BOOT_LED_ACTIVITY_MASK 0
-#endif
-
-// Doesn't make any sense for a RAM only binary
-#if !PICO_NO_FLASH
-static const uint32_t magic_token[] = {
-        0xf01681de, 0xbd729b29, 0xd359be7a,
-};
-
-static uint32_t __uninitialized_ram(magic_location)[count_of(magic_token)];
-
-// run at initialization time
-static void __attribute__((constructor)) boot_double_tap_check() {
-    for (uint i = 0; i < count_of(magic_token); i++) {
-        if (magic_location[i] != magic_token[i]) {
-            // Arm for 100 ms then disarm and continue booting
-            for (i = 0; i < count_of(magic_token); i++) {
-                magic_location[i] = magic_token[i];
-            }
-            busy_wait_us(100000);
-            magic_location[0] = 0;
-            return;
-        }
-    }
-
-    magic_location[0] = 0;
-    reset_usb_boot(USB_BOOT_LED_ACTIVITY_MASK, 0);
-}
-
-#endif

system/hello_double_tap/CMakeLists.txt

@@ -2,10 +2,17 @@ add_executable(hello_double_tap
         hello_double_tap.c
         )
 
-# Double tap reset into bootrom is injected by linking with the double_tap_usb_boot library
+# Double tap reset into bootrom is injected by linking with the
+# pico_bootsel_via_double_reset library
 target_link_libraries(hello_double_tap
         pico_stdlib
-        double_tap_usb_boot
+        pico_bootsel_via_double_reset
+        )
+
+# Entering the bootloader in this way also lets us specify a GPIO to be used
+# as a bootloader activity LED:
+target_compile_definitions(hello_double_tap PRIVATE
+	PICO_BOOTSEL_VIA_DOUBLE_RESET_ACTIVITY_LED=25
 	)
 
 pico_add_extra_outputs(hello_double_tap)

system/hello_double_tap/hello_double_tap.c

@@ -6,10 +6,14 @@
 
 #include "pico/stdlib.h"
 
-// This is a regular old LED blinking example, however it is linked with double_tap_usb_boot
+// This is a regular old LED blinking example, however it is linked with the
-// so pressing reset quickly twice, will reset into USB bootloader
+// `pico_bootsel_via_double_reset` library, so resetting the board twice
+// quickly will enter the USB bootloader. This is useful for boards which have
+// a reset button but no BOOTSEL, as long as you remember to always link the
+// `pico_bootsel_via_double_reset` library!
+
 int main() {
-    const uint LED_PIN = 21;
+    const uint LED_PIN = PICO_DEFAULT_LED_PIN;
     gpio_init(LED_PIN);
     gpio_set_dir(LED_PIN, GPIO_OUT);
     while (true) {