SDIO/SD 存储卡

FATFS fs;
FIL f;
FRESULT fr = f_mount(&fs, "", 1);        // 挂载
fr = f_open(&f, "0:/sensor.log", FA_OPEN_APPEND | FA_WRITE);

char line[64];
int n = snprintf(line, sizeof(line),
  "%s,%.2f,%.2f

", timestamp, temp, humi);
UINT bw = 0;
f_write(&f, line, n, &bw);               // 写一行
f_close(&f);                             // 及时关闭防丢

// 断电安全：日志可分段/定期 flush/双文件轮转