임베디드 스타트업 코드 분석 — Reset_Handler·Vector Table·SystemInit

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// startup_stm32f4xx.s 일부 (C 표현)
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__attribute__((section(".isr_vector")))
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const uint32_t vector_table[] = {
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    (uint32_t)&_estack,           // 0x00: Initial MSP
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    (uint32_t)Reset_Handler,      // 0x04: Reset
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    (uint32_t)NMI_Handler,        // 0x08: NMI
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    (uint32_t)HardFault_Handler,  // 0x0C
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    (uint32_t)MemManage_Handler,
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    (uint32_t)BusFault_Handler,
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    (uint32_t)UsageFault_Handler,
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    0, 0, 0, 0,
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    (uint32_t)SVC_Handler,        // 0x2C
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    (uint32_t)DebugMon_Handler,
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    0,
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    (uint32_t)PendSV_Handler,     // 0x38
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    (uint32_t)SysTick_Handler,    // 0x3C
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    // ... external IRQ
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};

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.global Reset_Handler
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.type Reset_Handler, %function
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Reset_Handler:
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    @ MSP는 hardware가 이미 적재했지만, code에서도 다시
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    ldr     r0, =_estack
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    mov     sp, r0
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    @ FPU enable (M4 + FPU 옵션)
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    ldr     r0, =0xE000ED88           @ CPACR
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    ldr     r1, [r0]
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    orr     r1, r1, #(0xF << 20)
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    str     r1, [r0]
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    @ SystemInit — 클럭, PLL
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    bl      SystemInit
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    @ .data 복사
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    ldr     r0, =_sidata
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    ldr     r1, =_sdata
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    ldr     r2, =_edata
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copy_data:
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    cmp     r1, r2
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    ittt    lt
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    ldrlt   r3, [r0], #4
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    strlt   r3, [r1], #4
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    blt     copy_data
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    @ .bss 클리어
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    ldr     r0, =_sbss
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    ldr     r1, =_ebss
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    mov     r2, #0
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zero_bss:
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    cmp     r0, r1
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    itt     lt
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    strlt   r2, [r0], #4
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    blt     zero_bss
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    @ C++ static constructor
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    bl      __libc_init_array
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    @ main
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    bl      main
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    @ main이 반환되면
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    b       .

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// newlib의 __libc_init_array 단순 구현
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extern void (*__init_array_start[])(void);
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extern void (*__init_array_end[])(void);
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void __libc_init_array(void) {
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    size_t count = __init_array_end - __init_array_start;
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    for (size_t i = 0; i < count; i++) {
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        __init_array_start[i]();
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    }
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}

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// 예 — C++ static 객체
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class Sensor {
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public:
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    Sensor() { initialize(); }   // __libc_init_array가 호출
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};
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static Sensor s_sensor;          // main 전에 생성됨

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void SystemInit(void) {
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    // FPU enable
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    SCB->CPACR |= ((3UL << 10*2) | (3UL << 11*2));
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    // Vector table 위치
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    SCB->VTOR = FLASH_BASE | 0x00;
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    // (보통 클럭은 main에서 설정)
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}

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#include <stdint.h>
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extern uint32_t _estack;
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extern uint32_t _sidata, _sdata, _edata;
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extern uint32_t _sbss, _ebss;
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extern void (*__init_array_start[])(void);
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extern void (*__init_array_end[])(void);
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extern int main(void);
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extern void SystemInit(void);
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void Default_Handler(void) {
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    while (1);
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}
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void Reset_Handler(void) {
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    SystemInit();
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    uint32_t *src = &_sidata;
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    uint32_t *dst = &_sdata;
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    while (dst < &_edata) *dst++ = *src++;
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    for (uint32_t *p = &_sbss; p < &_ebss; p++) *p = 0;
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    size_t count = __init_array_end - __init_array_start;
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    for (size_t i = 0; i < count; i++) {
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        __init_array_start[i]();
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    }
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    main();
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    while (1);
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}
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__attribute__((weak, alias("Default_Handler"))) void NMI_Handler(void);
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__attribute__((weak, alias("Default_Handler"))) void HardFault_Handler(void);
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// ... 나머지 IRQ도 weak alias
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__attribute__((section(".isr_vector"), used))
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void (* const vector_table[])(void) = {
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    (void (*)(void))((uint32_t)&_estack),
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    Reset_Handler,
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    NMI_Handler,
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    HardFault_Handler,
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    // ...
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};