*  @brief      Read raw gyro data directly from the registers.
 *  @param[out] data        Raw data in hardware units.
 *  @param[out] timestamp   Timestamp in milliseconds. Null if not needed.
 *  @return     0 if successful.
 */
int mpu_get_gyro_reg(short *data, unsigned long *timestamp)
{
    unsigned char tmp[6];

    if (!(st.chip_cfg.sensors & INV_XYZ_GYRO))
        return -1;

    if (i2c_read(st.hw->addr, st.reg->raw_gyro, 6, tmp))
        return -1;
    data[0] = (tmp[0] << 8) | tmp[1];
    data[1] = (tmp[2] << 8) | tmp[3];
    data[2] = (tmp[4] << 8) | tmp[5];
    if (timestamp)
        get_ms(timestamp);
    return 0;
}这是inv.mpu.c文件中读取陀螺仪原始数据的代码
问题1：timestamp有啥用？
问题2：get_ms（）函数在STM32中怎么实现？
求大神解答，先谢了