Cortex-MのstartupをCで書く例

startupは一般的にはアセンブラで書かれるのですが、Cortex-MではCで書くこともできるようで、startup.cが公開されています。以下（そのまま引用）（自分の覚書用）
GitHubの公開場所は以下
cortex-uni-startup/startup.c at master · pfalcon/cortex-uni-startup · GitHub
linker scriptもかなりシンプルなので、これからはこのstartupを使うつもりです。
このstartup.cと先ほどのLチカを組み合わせてビルドして、BluePillで動作することを確認した。

/*
 * Unified Cortex Startup - C startup file
 *
 * This file is in public domain
 *
 * Put together by Paul Sokolovsky based on article by Vanya Sergeev
 * http://dev.frozeneskimo.com/notes/cortex_cmsis/ , GNU ld documentation
 * and numerous other public resources.
 *
 */

#include <stdint.h>

/* Declare linker-defined symbols. The only thing of interest
   regarding these symbols is their *address*. uint32_t hints
   of alignment. */

extern uint32_t _end_text;
extern uint32_t _start_data;
extern uint32_t _end_data;
extern uint32_t _start_bss;
extern uint32_t _end_bss;
extern uint32_t _start_stack;
extern uint32_t _end_stack;

/* C main function */
extern int main(void);

/* Device-specific initialization function. Optional, any Cortex-M
   should be able to start up in its default mode on its own, though
   some may have errata for some peripherals (including PLL) which
   this function may "patch". */
extern void SystemInit(void);

void Dummy_Handler(void);

/* Cortex-M core interrupt handlers */
#define ALIAS(sym) __attribute__((weak, alias (sym)))

void Reset_Handler(void);
void NMI_Handler(void) ALIAS("Dummy_Handler");
void HardFault_Handler(void) ALIAS("Dummy_Handler");
void MemManage_Handler(void) ALIAS("Dummy_Handler");
void BusFault_Handler(void) ALIAS("Dummy_Handler");
void UsageFault_Handler(void) ALIAS("Dummy_Handler");
void SVC_Handler(void) ALIAS("Dummy_Handler");
void DebugMon_Handler(void) ALIAS("Dummy_Handler");
void PendSV_Handler(void) ALIAS("Dummy_Handler");
void SysTick_Handler(void) ALIAS("Dummy_Handler");


/* 16 standard Cortex-M vectors - these are present in every MCU */
void *core_vector_table[16] __attribute__ ((section(".cortex_vectors"))) = {
    // See http://sourceware.org/binutils/docs/ld/Source-Code-Reference.html
    // why the address is used here (if not intuitive)
    &_end_stack,
    Reset_Handler,
    NMI_Handler,
    HardFault_Handler,
    MemManage_Handler,
    BusFault_Handler,
    UsageFault_Handler,
    0,
    0,
    0,
    0,
    SVC_Handler,
    DebugMon_Handler,
    0,
    PendSV_Handler,
    SysTick_Handler,
};

/* Based on http://sourceware.org/binutils/docs/ld/Output-Section-LMA.html */
void Reset_Handler(void) {
    register uint32_t *src, *dst;

    /* Copy data section from flash to RAM */
    src = &_end_text;
    dst = &_start_data;
    while (dst < &_end_data)
        *dst++ = *src++;

    /* Clear the bss section, assumes .bss goes directly after .data */
    dst = &_start_bss;
    while (dst < &_end_bss)
        *dst++ = 0;

#ifndef NO_SYSTEMINIT
    SystemInit();
#endif
    main();
    while (1);
}

void Dummy_Handler(void) {
    /* Receiving an unexpected interrupt is considered a bug
       in the program. Let's make it very visible by just
       hanging the processing. Ignoring it by just returning
       may result in very complicated debugging sessions. */
    while (1);
}

以下がBluePill用のLチカメイン

/*
 * LED Blink Test for the STM32F103C8
 * 
 * original source :  Author : Chuck McManis
 * http://robotics.mcmanis.com/src/arm-blink/blink-example.html
 *
 */
#include <stdint.h>

#define GPIOC       0x40011000ul  
#define GPIOC_CRL  (*(uint32_t *)(GPIOC+0x00ul))
#define GPIOC_CRH  (*(uint32_t *)(GPIOC+0x04ul))
#define GPIOC_IDR  (*(uint32_t *)(GPIOC+0x08ul))
#define GPIOC_ODR  (*(uint32_t *)(GPIOC+0x0cul))
#define GPIOC_BSRR (*(uint32_t *)(GPIOC+0x10ul))
#define GPIOC_BRR  (*(uint32_t *)(GPIOC+0x14ul))
#define GPIOC_LCKR (*(uint32_t *)(GPIOC+0x14ul))

#define RCC_BASE      0x40021000ul
#define RCC_APB2ENR  (*(uint32_t *)(RCC_BASE + 0x18ul))
#define GPIOC_ENA     0x01 << 4   // C:bit4

#define GPIOC_13 13
#define GPIOC_8   8
#define OUT10MH 0x01 
#define CNF13_GENPP    0x00000000ul
#define MODE13_OUT10MH OUT10MH << ((GPIOC_13 - GPIOC_8) *4)
#define DELAY_TIME 300000

volatile int var;

void wait(int delay_time);
void blink(void);

void main()
{
  blink();

  // infinit loop
  while(1)
    ;
}


void blink(void){

  // setup GPIOC PORT
  RCC_APB2ENR = GPIOC_ENA; // Enable clocks to GPIOC
  GPIOC_CRH = CNF13_GENPP | MODE13_OUT10MH;  // set GPIOC_13 as OUTPUT
  GPIOC_BSRR = 1 << GPIOC_13 ; //LED off

  while (1) {
    GPIOC_BRR = 1 << GPIOC_13; // LED on
    wait(DELAY_TIME);

    GPIOC_BSRR = 1 << GPIOC_13 ; //LED off
    wait(DELAY_TIME);

  }
}

void wait(int delay_time){
  unsigned int i = delay_time;
  while(i--){
    asm("nop");
  }
}