임베디드 로깅 시스템 설계 — 레벨·버퍼·SWO·Deferred

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typedef enum { LOG_ERR, LOG_WARN, LOG_INFO, LOG_DBG } log_lvl_t;
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extern log_lvl_t g_log_level;
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#define LOG(lvl, fmt, ...) \
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    do { \
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        if ((lvl) <= g_log_level) \
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            log_emit(lvl, __FILE__, __LINE__, fmt, ##__VA_ARGS__); \
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    } while (0)
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#define LOG_ERR(fmt, ...)  LOG(0, fmt, ##__VA_ARGS__)
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#define LOG_WARN(fmt, ...) LOG(1, fmt, ##__VA_ARGS__)
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#define LOG_INFO(fmt, ...) LOG(2, fmt, ##__VA_ARGS__)
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#define LOG_DBG(fmt, ...)  LOG(3, fmt, ##__VA_ARGS__)

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#if !defined(LOG_LEVEL) || LOG_LEVEL < 3
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#  define LOG_DBG(fmt, ...) ((void)0)
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#endif

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#define LOG_RING 4096
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static uint8_t g_log[LOG_RING];
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static volatile uint16_t g_head, g_tail;
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static inline void log_push_bytes(const void *p, size_t n) {
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    const uint8_t *b = p;
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    for (size_t i = 0; i < n; i++) {
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        uint16_t next = (g_head + 1) & (LOG_RING - 1);
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        if (next == g_tail) g_tail = (g_tail + 1) & (LOG_RING - 1); /* drop oldest */
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        g_log[g_head] = b[i];
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        g_head = next;
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    }
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}

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struct log_rec {
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    uint32_t ts;        /* DWT CYCCNT */
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    uint16_t fmt_id;    /* host가 string으로 lookup */
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    uint8_t  argc;
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    uint8_t  pad;
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    uint32_t args[4];   /* up to 4 args */
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} __attribute__((packed));
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void log_binary(uint16_t fmt_id, int argc, ...) {
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    struct log_rec r = { DWT->CYCCNT, fmt_id, argc, 0, {0} };
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    va_list ap; va_start(ap, argc);
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    for (int i = 0; i < argc && i < 4; i++)
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        r.args[i] = va_arg(ap, uint32_t);
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    va_end(ap);
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    log_push_bytes(&r, sizeof(r));
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}
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#define LOG_B(fmt, ...) log_binary(__COUNTER__, ARG_COUNT(__VA_ARGS__), __VA_ARGS__)

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/* ITM 직접 — UART보다 100배 빠름 */
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static inline void swo_put(char c) {
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    if ((ITM->TER & 1) && (ITM->TCR & 1)) {
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        while (ITM->PORT[0].u32 == 0) ;
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        ITM->PORT[0].u8 = c;
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    }
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}
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void log_flush_swo(void) {
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    while (g_tail != g_head) {
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        swo_put(g_log[g_tail]);
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        g_tail = (g_tail + 1) & (LOG_RING - 1);
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    }
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}

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#include "SEGGER_RTT.h"
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SEGGER_RTT_Write(0, &rec, sizeof(rec));

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void idle_task(void) {
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    while (1) {
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        if (g_tail != g_head) log_flush_uart();
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        __WFI();
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    }
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}

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void hardfault_log_save(void) {
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    struct crash_log *cl = (void*)BACKUP_SRAM;
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    cl->magic = 0xFA17;
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    cl->head = g_head;
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    cl->tail = g_tail;
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    memcpy(cl->buf, g_log, LOG_RING);
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    NVIC_SystemReset();
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}
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void boot_check_crash(void) {
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    struct crash_log *cl = (void*)BACKUP_SRAM;
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    if (cl->magic == 0xFA17) {
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        printf("Previous crash log:\n");
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        log_dump_buf(cl->buf, cl->head, cl->tail);
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        cl->magic = 0;
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    }
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}

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#define LOG_TAG_NET   1
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#define LOG_TAG_FS    2
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#define LOG_TAG_UI    3
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#define LOG_NET(lvl, fmt, ...) \
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    do { if (lvl <= g_log_level && (g_log_tag_mask & (1 << LOG_TAG_NET))) \
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            log_emit(lvl, LOG_TAG_NET, fmt, ##__VA_ARGS__); } while (0)

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void TIM2_IRQHandler(void) {
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    HAL_GPIO_TogglePin(GPIOC, GPIO_PIN_13);
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    printf("tick %lu\n", HAL_GetTick());  /* ~1ms — 다음 IRQ가 떨어짐 */
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}

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void TIM2_IRQHandler(void) {
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    TIM2->SR &= ~TIM_SR_UIF;
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    HAL_GPIO_TogglePin(GPIOC, GPIO_PIN_13);
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    LOG_B("tick %u", HAL_GetTick());      /* ~50 cycle */
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}

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__disable_irq();
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LOG_INFO("entering critical");   /* IRQ disable 동안 UART 못 보냄 */
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do_critical();
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__enable_irq();

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LOG_INFO("Entered process_packet with channel=%d, size=%d", ch, sz);