marlin/buildroot/share/PlatformIO/variants/MARLIN_ARTILLERY_RUBY/startup.S

 /**
  ******************************************************************************
  * @file      startup_stm32f401xc.s
  * @author    MCD Application Team
  * @version   V2.4.2
  * @date      13-November-2015
  * @brief     STM32F401xCxx Devices vector table for GCC based toolchains.
  *            This module performs:
  *                - Set the initial SP
  *                - Set the initial PC == Reset_Handler,
  *                - Set the vector table entries with the exceptions ISR address
  *                - Branches to main in the C library (which eventually
  *                  calls main()).
  *            After Reset the Cortex-M4 processor is in Thread mode,
  *            priority is Privileged, and the Stack is set to Main.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2015 STMicroelectronics
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  */

  .syntax unified
  .cpu cortex-m4
  .fpu softvfp
  .thumb

/**
 * @brief  This is the code that gets called when the processor first
 *          starts execution following a reset event. Only the absolutely
 *          necessary set is performed, after which the application
 *          supplied main() routine is called.
 * @param  None
 * @retval : None
 */

  .section  .text.Reset_Handler
  .globl Reset_Handler
  .type  Reset_Handler, %function
Reset_Handler:
/* Check for magic code at the end of SRAM to detemine whether to jump to DFU */
  ldr   r0, =0x2000FFF0 // End of SRAM for your CPU
  ldr   r1, =0xDEADBEEF
  ldr   r2, [r0, #0]
  str   r0, [r0, #0] // Invalidate
  cmp   r2, r1
  beq   Jump_To_DFU

/* Original Reset_Handler code */
  ldr   sp, =_estack      /* set stack pointer */

/* Copy the data segment initializers from flash to SRAM */
  movs  r1, #0
  b  LoopCopyDataInit

CopyDataInit:
  ldr  r3, =_sidata
  ldr  r3, [r3, r1]
  str  r3, [r0, r1]
  adds  r1, r1, #4

LoopCopyDataInit:
  ldr  r0, =_sdata
  ldr  r3, =_edata
  adds  r2, r0, r1
  cmp  r2, r3
  bcc  CopyDataInit
  ldr  r2, =_sbss
  b  LoopFillZerobss
/* Zero fill the bss segment. */
FillZerobss:
  movs  r3, #0
  str  r3, [r2], #4

LoopFillZerobss:
  ldr  r3, = _ebss
  cmp  r2, r3
  bcc  FillZerobss

/* Call the clock system intitialization function.*/
  bl  SystemInit
/* Call static constructors */
  bl __libc_init_array
/* Call the application's entry point.*/
  bl  main
  bx  lr

Jump_To_DFU:
  ldr   r0, =0x40023844 // RCC_APB2ENR
  ldr   r1, =0x00004000 // ENABLE SYSCFG CLOCK
  str   r1, [r0, #0]
  ldr   r0, =0x40013800 // SYSCFG_MEMRMP
  ldr   r1, =0x00000001 // MAP ROM AT ZERO
  str   r1, [r0, #0]
  ldr   r0, =0x1FFF0000 // ROM BASE
  ldr   sp, [r0, #0]    // SP @ +0
  ldr   r0, [r0, #4]    // PC @ +4
  bx    r0
.size  Reset_Handler, .-Reset_Handler

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/