임베디드 Trace 비교 — RTT·ITM·SWO·ETM·Semihosting 선택

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// SYS_WRITE0: NUL-terminated string을 호스트 stdout으로
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static inline void semihost_puts(const char *s) {
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    register const char *r1 asm("r1") = s;
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    register int r0 asm("r0") = 0x04;     // SYS_WRITE0
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    asm volatile("bkpt #0xAB" : "+r"(r0) : "r"(r1));
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}
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void main() {
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    semihost_puts("Hello, host!\n");
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    ...
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}

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(openocd) arm semihosting enable

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// newlib retarget
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extern "C" int _write(int fd, char *ptr, int len) {
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    for (int i = 0; i < len; i++) {
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        register int r0 asm("r0") = 0x03;          // SYS_WRITEC
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        register const char *r1 asm("r1") = &ptr[i];
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        asm volatile("bkpt #0xAB" : "+r"(r0) : "r"(r1));
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    }
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    return len;
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}

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// ITM 활성화 (한 번)
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void itm_init(uint32_t core_clock_hz, uint32_t swo_baud) {
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    // 트레이스 핀 enable
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    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
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    // TPIU pin protocol = NRZ (UART-like SWO)
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    TPI->SPPR = 0x02;
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    // SWO baud rate: prescaler = core_clock / swo_baud - 1
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    TPI->ACPR = (core_clock_hz / swo_baud) - 1;
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    // ITM unlock
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    ITM->LAR = 0xC5ACCE55;
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    // ITM enable, stim port 0 enable
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    ITM->TCR = ITM_TCR_TraceBusID_Msk | ITM_TCR_SWOENA_Msk |
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               ITM_TCR_DWTENA_Msk | ITM_TCR_ITMENA_Msk;
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    ITM->TER = 0xFFFFFFFF;   // 모든 32 stim port
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    // formatter disable
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    TPI->FFCR = 0x100;
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}
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static inline void itm_putchar(char c) {
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    if ((ITM->TCR & ITM_TCR_ITMENA_Msk) == 0) return;
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    if ((ITM->TER & 1) == 0) return;
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    while ((ITM->PORT[0].u32 & 1) == 0);   // FIFO busy?
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    ITM->PORT[0].u8 = c;
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}

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extern "C" int _write(int fd, char *ptr, int len) {
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    for (int i = 0; i < len; i++) itm_putchar(ptr[i]);
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    return len;
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}

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(openocd) tpiu config internal /tmp/swo.log uart off 168000000 2000000
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                              ^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^ ^^^^^^^
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                              파일 (또는 :port)        core_clock swo_baud
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(openocd) itm port 0 on

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(JLink) SWOSpeed 2000000
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(JLink) SWOSetClk 168000000     # 코어 클럭
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(JLink) SWOStart
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(JLink) SWORead             # 한번 읽기

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static inline void itm_send_u32(uint8_t port, uint32_t value) {
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    while ((ITM->PORT[port].u32 & 1) == 0);
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    ITM->PORT[port].u32 = value;
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}
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// 채널 0 = stdout
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itm_putchar('a');
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// 채널 1 = 센서 raw
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itm_send_u32(1, sensor_value);

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struct {
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    char id[16];           // "SEGGER RTT\0"
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    uint32_t max_up;       // up 채널 개수
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    uint32_t max_down;     // down 채널 개수
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    SEGGER_RTT_BUFFER_UP up[2];
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    SEGGER_RTT_BUFFER_DOWN down[2];
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} _SEGGER_RTT;

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#include "SEGGER_RTT.h"
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void main() {
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    SEGGER_RTT_Init();         // 또는 자동 초기화 (zero-init)
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    SEGGER_RTT_printf(0, "boot\n");
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    while (1) {
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        SEGGER_RTT_printf(0, "tick=%u\n", HAL_GetTick());
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        HAL_Delay(1000);
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    }
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}

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(gdb) monitor exec SetRTTSearchRanges 0x20000000 0x10000
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(gdb) monitor exec SetRTTAddr 0x20000000

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(openocd) rtt setup 0x20000000 0x10000 "SEGGER RTT"
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(openocd) rtt start
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(openocd) rtt server start 9090 0

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// 채널 1을 binary 센서 데이터로
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SEGGER_RTT_ConfigUpBuffer(1, "Sensor", buf, sizeof(buf),
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                          SEGGER_RTT_MODE_NO_BLOCK_SKIP);
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SEGGER_RTT_Write(1, sensor_raw, 256);

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// 호스트가 보낸 명령 받기
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char cmd[32];
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int n = SEGGER_RTT_Read(0, cmd, sizeof(cmd));
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if (n > 0) process_command(cmd, n);

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void uart_putchar(char c) {
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    while (!(USART1->SR & USART_SR_TXE));
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    USART1->DR = c;
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}

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extern "C" int _write(int fd, char *buf, int len) {
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    // RTT가 connected면 RTT로, 아니면 UART로 폴백
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    if (SEGGER_RTT_HasData(0) || JLINK_CONNECTED) {
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        return SEGGER_RTT_Write(0, buf, len);
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    }
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    for (int i = 0; i < len; i++) uart_putchar(buf[i]);
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    return len;
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}

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// 채널 0 (up) = 로그
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// 채널 1 (up) = 센서 binary
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// 채널 0 (down) = 셸 명령
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void shell_loop() {
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    char line[64]; int n = 0;
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    while (1) {
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        int c = SEGGER_RTT_GetKey();
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        if (c < 0) continue;
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        if (c == '\n' || c == '\r') {
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            line[n] = '\0';
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            handle_cmd(line);
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            n = 0;
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        } else if (n < sizeof(line) - 1) {
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            line[n++] = c;
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            SEGGER_RTT_putchar(0, c);    // echo
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        }
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    }
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}
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void handle_cmd(const char *line) {
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    if (strcmp(line, "stats") == 0) {
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        SEGGER_RTT_printf(0, "ticks=%u, uptime=%u\n",
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                          HAL_GetTick(), get_uptime());
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    } else if (strncmp(line, "set ", 4) == 0) {
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        ...
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    }
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}