Refactor `bootloader_jump()` implementations (#15450)

* Refactor `bootloader_jump()` implementations

* Fix tests?

* Rename `atmel-samba` to `md-boot`

7 files changed, 332 insertions, 293 deletions

diff --git a/platforms/avr/bootloader.c b/platforms/avr/bootloader.c
deleted file mode 100644
index c0272903b8..0000000000
--- a/platforms/avr/bootloader.c
+++ /dev/null
@@ -1,293 +0,0 @@
-#include <stdint.h>
-#include <stdbool.h>
-#include <avr/io.h>
-#include <avr/eeprom.h>
-#include <avr/interrupt.h>
-#include <avr/wdt.h>
-#include <util/delay.h>
-#include "bootloader.h"
-#include <avr/boot.h>
-
-#ifdef PROTOCOL_LUFA
-#    include <LUFA/Drivers/USB/USB.h>
-#endif
-
-/** \brief Bootloader Size in *bytes*
- *
- * AVR Boot section size are defined by setting BOOTSZ fuse in fact. Consult with your MCU datasheet.
- * Note that 'Word'(2 bytes) size and address are used in datasheet while TMK uses 'Byte'.
- *
- * Size of Bootloaders in bytes:
- *   Atmel DFU loader(ATmega32U4)   4096
- *   Atmel DFU loader(AT90USB128)   8192
- *   LUFA bootloader(ATmega32U4)    4096
- *   Arduino Caterina(ATmega32U4)   4096
- *   USBaspLoader(ATmega***)        2048
- *   Teensy   halfKay(ATmega32U4)   512
- *   Teensy++ halfKay(AT90USB128)   1024
- *
- * AVR Boot section is located at the end of Flash memory like the followings.
- *
- * byte     Atmel/LUFA(ATMega32u4)          byte     Atmel(AT90SUB128)
- * 0x0000   +---------------+               0x00000  +---------------+
- *          |               |                        |               |
- *          |               |                        |               |
- *          |  Application  |                        |  Application  |
- *          |               |                        |               |
- *          =               =                        =               =
- *          |               | 32KB-4KB               |               | 128KB-8KB
- * 0x7000   +---------------+               0x1E000  +---------------+
- *          |  Bootloader   | 4KB                    |  Bootloader   | 8KB
- * 0x7FFF   +---------------+               0x1FFFF  +---------------+
- *
- *
- * byte     Teensy(ATMega32u4)              byte     Teensy++(AT90SUB128)
- * 0x0000   +---------------+               0x00000  +---------------+
- *          |               |                        |               |
- *          |               |                        |               |
- *          |  Application  |                        |  Application  |
- *          |               |                        |               |
- *          =               =                        =               =
- *          |               | 32KB-512B              |               | 128KB-1KB
- * 0x7E00   +---------------+               0x1FC00  +---------------+
- *          |  Bootloader   | 512B                   |  Bootloader   | 1KB
- * 0x7FFF   +---------------+               0x1FFFF  +---------------+
- */
-#define FLASH_SIZE (FLASHEND + 1L)
-
-#if !defined(BOOTLOADER_SIZE)
-uint16_t bootloader_start;
-#endif
-
-// compatibility between ATMega8 and ATMega88
-#if !defined(MCUCSR)
-#    if defined(MCUSR)
-#        define MCUCSR MCUSR
-#    endif
-#endif
-
-/** \brief Entering the Bootloader via Software
- *
- * http://www.fourwalledcubicle.com/files/LUFA/Doc/120730/html/_page__software_bootloader_start.html
- */
-#define BOOTLOADER_RESET_KEY 0xB007B007
-uint32_t reset_key __attribute__((section(".noinit,\"aw\",@nobits;")));
-
-/** \brief initialize MCU status by watchdog reset
- *
- * FIXME: needs doc
- */
-__attribute__((weak)) void bootloader_jump(void) {
-#if !defined(BOOTLOADER_SIZE)
-    uint8_t high_fuse = boot_lock_fuse_bits_get(GET_HIGH_FUSE_BITS);
-
-    if (high_fuse & ~(FUSE_BOOTSZ0 & FUSE_BOOTSZ1)) {
-        bootloader_start = (FLASH_SIZE - 512) >> 1;
-    } else if (high_fuse & ~(FUSE_BOOTSZ1)) {
-        bootloader_start = (FLASH_SIZE - 1024) >> 1;
-    } else if (high_fuse & ~(FUSE_BOOTSZ0)) {
-        bootloader_start = (FLASH_SIZE - 2048) >> 1;
-    } else {
-        bootloader_start = (FLASH_SIZE - 4096) >> 1;
-    }
-#endif
-
-    // Something like this might work, but it compiled larger than the block above
-    // bootloader_start = FLASH_SIZE - (256 << (~high_fuse & 0b110 >> 1));
-
-#if defined(BOOTLOADER_HALFKAY)
-    //  http://www.pjrc.com/teensy/jump_to_bootloader.html
-    cli();
-    // disable watchdog, if enabled (it's not)
-    // disable all peripherals
-    // a shutdown call might make sense here
-    UDCON  = 1;
-    USBCON = (1 << FRZCLK);  // disable USB
-    UCSR1B = 0;
-    _delay_ms(5);
-#    if defined(__AVR_AT90USB162__)  // Teensy 1.0
-    EIMSK  = 0;
-    PCICR  = 0;
-    SPCR   = 0;
-    ACSR   = 0;
-    EECR   = 0;
-    TIMSK0 = 0;
-    TIMSK1 = 0;
-    UCSR1B = 0;
-    DDRB   = 0;
-    DDRC   = 0;
-    DDRD   = 0;
-    PORTB  = 0;
-    PORTC  = 0;
-    PORTD  = 0;
-    asm volatile("jmp 0x3E00");
-#    elif defined(__AVR_ATmega32U4__)   // Teensy 2.0
-    EIMSK  = 0;
-    PCICR  = 0;
-    SPCR   = 0;
-    ACSR   = 0;
-    EECR   = 0;
-    ADCSRA = 0;
-    TIMSK0 = 0;
-    TIMSK1 = 0;
-    TIMSK3 = 0;
-    TIMSK4 = 0;
-    UCSR1B = 0;
-    TWCR   = 0;
-    DDRB   = 0;
-    DDRC   = 0;
-    DDRD   = 0;
-    DDRE   = 0;
-    DDRF   = 0;
-    TWCR   = 0;
-    PORTB  = 0;
-    PORTC  = 0;
-    PORTD  = 0;
-    PORTE  = 0;
-    PORTF  = 0;
-    asm volatile("jmp 0x7E00");
-#    elif defined(__AVR_AT90USB646__)   // Teensy++ 1.0
-    EIMSK  = 0;
-    PCICR  = 0;
-    SPCR   = 0;
-    ACSR   = 0;
-    EECR   = 0;
-    ADCSRA = 0;
-    TIMSK0 = 0;
-    TIMSK1 = 0;
-    TIMSK2 = 0;
-    TIMSK3 = 0;
-    UCSR1B = 0;
-    TWCR   = 0;
-    DDRA   = 0;
-    DDRB   = 0;
-    DDRC   = 0;
-    DDRD   = 0;
-    DDRE   = 0;
-    DDRF   = 0;
-    PORTA  = 0;
-    PORTB  = 0;
-    PORTC  = 0;
-    PORTD  = 0;
-    PORTE  = 0;
-    PORTF  = 0;
-    asm volatile("jmp 0xFC00");
-#    elif defined(__AVR_AT90USB1286__)  // Teensy++ 2.0
-    EIMSK  = 0;
-    PCICR  = 0;
-    SPCR   = 0;
-    ACSR   = 0;
-    EECR   = 0;
-    ADCSRA = 0;
-    TIMSK0 = 0;
-    TIMSK1 = 0;
-    TIMSK2 = 0;
-    TIMSK3 = 0;
-    UCSR1B = 0;
-    TWCR   = 0;
-    DDRA   = 0;
-    DDRB   = 0;
-    DDRC   = 0;
-    DDRD   = 0;
-    DDRE   = 0;
-    DDRF   = 0;
-    PORTA  = 0;
-    PORTB  = 0;
-    PORTC  = 0;
-    PORTD  = 0;
-    PORTE  = 0;
-    PORTF  = 0;
-    asm volatile("jmp 0x1FC00");
-#    endif
-
-#elif defined(BOOTLOADER_CATERINA)
-    // this block may be optional
-    // TODO: figure it out
-
-    uint16_t *const bootKeyPtr = (uint16_t *)0x0800;
-
-    // Value used by Caterina bootloader use to determine whether to run the
-    // sketch or the bootloader programmer.
-    uint16_t bootKey = 0x7777;
-
-    *bootKeyPtr = bootKey;
-
-    // setup watchdog timeout
-    wdt_enable(WDTO_60MS);
-
-    while (1) {
-    }  // wait for watchdog timer to trigger
-
-#elif defined(BOOTLOADER_USBASP)
-    // Taken with permission of Stephan Baerwolf from https://github.com/tinyusbboard/API/blob/master/apipage.c
-    wdt_enable(WDTO_15MS);
-    wdt_reset();
-    asm volatile("cli                    \n\t"
-                 "ldi    r29 ,       %[ramendhi] \n\t"
-                 "ldi    r28 ,       %[ramendlo] \n\t"
-#    if (FLASHEND > 131071)
-                 "ldi    r18 ,       %[bootaddrhi]   \n\t"
-                 "st     Y+,         r18     \n\t"
-#    endif
-                 "ldi    r18 ,       %[bootaddrme]   \n\t"
-                 "st     Y+,     r18     \n\t"
-                 "ldi    r18 ,       %[bootaddrlo]   \n\t"
-                 "st     Y+,     r18     \n\t"
-                 "out    %[mcucsrio],    __zero_reg__    \n\t"
-                 "bootloader_startup_loop%=:         \n\t"
-                 "rjmp bootloader_startup_loop%=     \n\t"
-                 :
-                 : [mcucsrio] "I"(_SFR_IO_ADDR(MCUCSR)),
-#    if (FLASHEND > 131071)
-                   [ramendhi] "M"(((RAMEND - 2) >> 8) & 0xff), [ramendlo] "M"(((RAMEND - 2) >> 0) & 0xff), [bootaddrhi] "M"((((FLASH_SIZE - BOOTLOADER_SIZE) >> 1) >> 16) & 0xff),
-#    else
-                   [ramendhi] "M"(((RAMEND - 1) >> 8) & 0xff), [ramendlo] "M"(((RAMEND - 1) >> 0) & 0xff),
-#    endif
-                   [bootaddrme] "M"((((FLASH_SIZE - BOOTLOADER_SIZE) >> 1) >> 8) & 0xff), [bootaddrlo] "M"((((FLASH_SIZE - BOOTLOADER_SIZE) >> 1) >> 0) & 0xff));
-
-#else  // Assume remaining boards are DFU, even if the flag isn't set
-
-#    if !(defined(__AVR_ATmega32A__) || defined(__AVR_ATmega328P__) || defined(__AVR_ATmega328__) || defined(__AVR_ATtiny85__))  // no USB - maybe BOOTLOADER_BOOTLOADHID instead though?
-    UDCON  = 1;
-    USBCON = (1 << FRZCLK);  // disable USB
-    UCSR1B = 0;
-    _delay_ms(5);  // 5 seems to work fine
-#    endif
-
-#    ifdef BOOTLOADER_BOOTLOADHID
-    // force bootloadHID to stay in bootloader mode, so that it waits
-    // for a new firmware to be flashed
-    eeprom_write_byte((uint8_t *)1, 0x00);
-#    endif
-
-    // watchdog reset
-    reset_key = BOOTLOADER_RESET_KEY;
-    wdt_enable(WDTO_250MS);
-    for (;;)
-        ;
-#endif
-}
-
-/* this runs before main() */
-void bootloader_jump_after_watchdog_reset(void) __attribute__((used, naked, section(".init3")));
-void bootloader_jump_after_watchdog_reset(void) {
-#ifndef BOOTLOADER_HALFKAY
-    if ((MCUCSR & (1 << WDRF)) && reset_key == BOOTLOADER_RESET_KEY) {
-        reset_key = 0;
-
-        // My custom USBasploader requires this to come up.
-        MCUCSR = 0;
-
-        // Seems like Teensy halfkay loader requires clearing WDRF and disabling watchdog.
-        MCUCSR &= ~(1 << WDRF);
-        wdt_disable();
-
-// This is compled into 'icall', address should be in word unit, not byte.
-#    ifdef BOOTLOADER_SIZE
-        ((void (*)(void))((FLASH_SIZE - BOOTLOADER_SIZE) >> 1))();
-#    else
-        asm("ijmp" ::"z"(bootloader_start));
-#    endif
-    }
-#endif
-}
diff --git a/platforms/avr/bootloaders/bootloadhid.c b/platforms/avr/bootloaders/bootloadhid.c
new file mode 100644
index 0000000000..8d18114613
--- /dev/null
+++ b/platforms/avr/bootloaders/bootloadhid.c
@@ -0,0 +1,34 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+#include <avr/eeprom.h>
+#include <avr/wdt.h>
+
+__attribute__((weak))
+void bootloader_jump(void) {
+    // force bootloadHID to stay in bootloader mode, so that it waits
+    // for a new firmware to be flashed
+    // NOTE: this byte is part of QMK's "magic number" - changing it causes the EEPROM to be re-initialized
+    // thus every time the device is flashed the EEPROM will be wiped
+    eeprom_write_byte((uint8_t *)1, 0x00);
+
+    // watchdog reset
+    wdt_enable(WDTO_250MS);
+    for (;;)
+        ;
+}
diff --git a/platforms/avr/bootloaders/caterina.c b/platforms/avr/bootloaders/caterina.c
new file mode 100644
index 0000000000..1b43ed4e44
--- /dev/null
+++ b/platforms/avr/bootloaders/caterina.c
@@ -0,0 +1,39 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+#include <avr/wdt.h>
+
+__attribute__((weak))
+void bootloader_jump(void) {
+    // this block may be optional
+    // TODO: figure it out
+
+    uint16_t *const bootKeyPtr = (uint16_t *)0x0800;
+
+    // Value used by Caterina bootloader use to determine whether to run the
+    // sketch or the bootloader programmer.
+    uint16_t bootKey = 0x7777;
+
+    *bootKeyPtr = bootKey;
+
+    // setup watchdog timeout
+    wdt_enable(WDTO_60MS);
+
+    // wait for watchdog timer to trigger
+    while (1) { }
+}
diff --git a/platforms/avr/bootloaders/dfu.c b/platforms/avr/bootloaders/dfu.c
new file mode 100644
index 0000000000..bdf5908934
--- /dev/null
+++ b/platforms/avr/bootloaders/dfu.c
@@ -0,0 +1,53 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+#include <avr/wdt.h>
+#include <util/delay.h>
+
+#define FLASH_SIZE (FLASHEND + 1L)
+
+/** \brief Entering the Bootloader via Software
+ *
+ * http://www.fourwalledcubicle.com/files/LUFA/Doc/120730/html/_page__software_bootloader_start.html
+ */
+#define BOOTLOADER_RESET_KEY 0xB007B007
+uint32_t reset_key __attribute__((section(".noinit,\"aw\",@nobits;")));
+
+__attribute__((weak))
+void bootloader_jump(void) {
+    UDCON  = 1;
+    USBCON = (1 << FRZCLK);  // disable USB
+    UCSR1B = 0;
+    _delay_ms(5);  // 5 seems to work fine
+
+    // watchdog reset
+    reset_key = BOOTLOADER_RESET_KEY;
+    wdt_enable(WDTO_250MS);
+    for (;;)
+        ;
+}
+
+/* this runs before main() */
+void bootloader_jump_after_watchdog_reset(void) __attribute__((used, naked, section(".init3")));
+void bootloader_jump_after_watchdog_reset(void) {
+    if ((MCUSR & (1 << WDRF)) && reset_key == BOOTLOADER_RESET_KEY) {
+        reset_key = 0;
+
+        ((void (*)(void))((FLASH_SIZE - BOOTLOADER_SIZE) >> 1))();
+    }
+}
diff --git a/platforms/avr/bootloaders/halfkay.c b/platforms/avr/bootloaders/halfkay.c
new file mode 100644
index 0000000000..abef86980b
--- /dev/null
+++ b/platforms/avr/bootloaders/halfkay.c
@@ -0,0 +1,129 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+#include <avr/interrupt.h>
+#include <util/delay.h>
+
+__attribute__((weak))
+void bootloader_jump(void) {
+    // http://www.pjrc.com/teensy/jump_to_bootloader.html
+
+    cli();
+    // disable watchdog, if enabled (it's not)
+    // disable all peripherals
+    // a shutdown call might make sense here
+    UDCON  = 1;
+    USBCON = (1 << FRZCLK);  // disable USB
+    UCSR1B = 0;
+    _delay_ms(5);
+
+#if defined(__AVR_AT90USB162__)  // Teensy 1.0
+    EIMSK  = 0;
+    PCICR  = 0;
+    SPCR   = 0;
+    ACSR   = 0;
+    EECR   = 0;
+    TIMSK0 = 0;
+    TIMSK1 = 0;
+    UCSR1B = 0;
+    DDRB   = 0;
+    DDRC   = 0;
+    DDRD   = 0;
+    PORTB  = 0;
+    PORTC  = 0;
+    PORTD  = 0;
+    asm volatile("jmp 0x3E00");
+#elif defined(__AVR_ATmega32U4__)   // Teensy 2.0
+    EIMSK  = 0;
+    PCICR  = 0;
+    SPCR   = 0;
+    ACSR   = 0;
+    EECR   = 0;
+    ADCSRA = 0;
+    TIMSK0 = 0;
+    TIMSK1 = 0;
+    TIMSK3 = 0;
+    TIMSK4 = 0;
+    UCSR1B = 0;
+    TWCR   = 0;
+    DDRB   = 0;
+    DDRC   = 0;
+    DDRD   = 0;
+    DDRE   = 0;
+    DDRF   = 0;
+    TWCR   = 0;
+    PORTB  = 0;
+    PORTC  = 0;
+    PORTD  = 0;
+    PORTE  = 0;
+    PORTF  = 0;
+    asm volatile("jmp 0x7E00");
+#elif defined(__AVR_AT90USB646__)   // Teensy++ 1.0
+    EIMSK  = 0;
+    PCICR  = 0;
+    SPCR   = 0;
+    ACSR   = 0;
+    EECR   = 0;
+    ADCSRA = 0;
+    TIMSK0 = 0;
+    TIMSK1 = 0;
+    TIMSK2 = 0;
+    TIMSK3 = 0;
+    UCSR1B = 0;
+    TWCR   = 0;
+    DDRA   = 0;
+    DDRB   = 0;
+    DDRC   = 0;
+    DDRD   = 0;
+    DDRE   = 0;
+    DDRF   = 0;
+    PORTA  = 0;
+    PORTB  = 0;
+    PORTC  = 0;
+    PORTD  = 0;
+    PORTE  = 0;
+    PORTF  = 0;
+    asm volatile("jmp 0xFC00");
+#elif defined(__AVR_AT90USB1286__)  // Teensy++ 2.0
+    EIMSK  = 0;
+    PCICR  = 0;
+    SPCR   = 0;
+    ACSR   = 0;
+    EECR   = 0;
+    ADCSRA = 0;
+    TIMSK0 = 0;
+    TIMSK1 = 0;
+    TIMSK2 = 0;
+    TIMSK3 = 0;
+    UCSR1B = 0;
+    TWCR   = 0;
+    DDRA   = 0;
+    DDRB   = 0;
+    DDRC   = 0;
+    DDRD   = 0;
+    DDRE   = 0;
+    DDRF   = 0;
+    PORTA  = 0;
+    PORTB  = 0;
+    PORTC  = 0;
+    PORTD  = 0;
+    PORTE  = 0;
+    PORTF  = 0;
+    asm volatile("jmp 0x1FC00");
+#endif
+}
diff --git a/platforms/avr/bootloaders/none.c b/platforms/avr/bootloaders/none.c
new file mode 100644
index 0000000000..8af151c04d
--- /dev/null
+++ b/platforms/avr/bootloaders/none.c
@@ -0,0 +1,20 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+__attribute__((weak))
+void bootloader_jump(void) { }
diff --git a/platforms/avr/bootloaders/usbasploader.c b/platforms/avr/bootloaders/usbasploader.c
new file mode 100644
index 0000000000..b3e9b2d72d
--- /dev/null
+++ b/platforms/avr/bootloaders/usbasploader.c
@@ -0,0 +1,57 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "bootloader.h"
+
+#include <avr/wdt.h>
+
+#define FLASH_SIZE (FLASHEND + 1L)
+
+#if !defined(MCUCSR)
+#    if defined(MCUSR)
+#        define MCUCSR MCUSR
+#    endif
+#endif
+
+__attribute__((weak))
+void bootloader_jump(void) {
+    // Taken with permission of Stephan Baerwolf from https://github.com/tinyusbboard/API/blob/master/apipage.c
+
+    wdt_enable(WDTO_15MS);
+    wdt_reset();
+    asm volatile("cli                    \n\t"
+                 "ldi    r29 ,       %[ramendhi] \n\t"
+                 "ldi    r28 ,       %[ramendlo] \n\t"
+#if (FLASHEND > 131071)
+                 "ldi    r18 ,       %[bootaddrhi]   \n\t"
+                 "st     Y+,         r18     \n\t"
+#endif
+                 "ldi    r18 ,       %[bootaddrme]   \n\t"
+                 "st     Y+,     r18     \n\t"
+                 "ldi    r18 ,       %[bootaddrlo]   \n\t"
+                 "st     Y+,     r18     \n\t"
+                 "out    %[mcucsrio],    __zero_reg__    \n\t"
+                 "bootloader_startup_loop%=:         \n\t"
+                 "rjmp bootloader_startup_loop%=     \n\t"
+                 :
+                 : [mcucsrio] "I"(_SFR_IO_ADDR(MCUCSR)),
+#if (FLASHEND > 131071)
+                   [ramendhi] "M"(((RAMEND - 2) >> 8) & 0xff), [ramendlo] "M"(((RAMEND - 2) >> 0) & 0xff), [bootaddrhi] "M"((((FLASH_SIZE - BOOTLOADER_SIZE) >> 1) >> 16) & 0xff),
+#else
+                   [ramendhi] "M"(((RAMEND - 1) >> 8) & 0xff), [ramendlo] "M"(((RAMEND - 1) >> 0) & 0xff),
+#endif
+                   [bootaddrme] "M"((((FLASH_SIZE - BOOTLOADER_SIZE) >> 1) >> 8) & 0xff), [bootaddrlo] "M"((((FLASH_SIZE - BOOTLOADER_SIZE) >> 1) >> 0) & 0xff));
+}