为什么用串口接收电机返回的指令会分包打印啊？

static void servo_uart_protov4_proc(uint8_t dat)
{
    rt_base_t level;
    if (mxProtoV4Fifo.left_cnt > 0) {
        if(mxProtoV4Fifo.left_cnt == 1)
          {
            servoUartPv4 = 1;
          }
            mxProtoV4Fifo.left_cnt--; 
            mxProtoV4Fifo.buff[mxProtoV4Fifo.add_cnt++] = dat;
            if(servoUartPv4 == 1)
            {    
            //level = rt_hw_interrupt_disable();
                //rt_mutex_take(dynamic_mutex, RT_WAITING_FOREVER);
                for (int8_t i = 0; i < 3+datalong; i++)
                {
                    rt_kprintf("%02X ",mxProtoV4Fifo.buff[i]);
                }
                 rt_kprintf("\n");
               // rt_mutex_release(dynamic_mutex);
            //  rt_hw_interrupt_enable(level);
                   datalong = 0;
                   mxProtoV4Fifo.add_cnt = 0;
                   servoUartPv4 = 0;
            }
    } else {
        if (mxProtoV4Fifo.add_cnt == 0) {
            if (dat == 0xFF) {
                mxProtoV4Fifo.buff[mxProtoV4Fifo.add_cnt++] = dat;
            }else{
                return ;
            }
        } else if (mxProtoV4Fifo.add_cnt == 1) {
            if (dat == 0xF5) {
                mxProtoV4Fifo.buff[mxProtoV4Fifo.add_cnt++] = dat;
            } else {
                mxProtoV4Fifo.add_cnt = 0;
            }
        } else if (mxProtoV4Fifo.add_cnt == 2) {   
            if (dat == mxp_fal_param_db->sid_pos || dat == 253 || dat == 254) {
                mxProtoV4Fifo.buff[mxProtoV4Fifo.add_cnt++] = dat;
            } else {
                mxProtoV4Fifo.add_cnt = 0;
            }
        } else if (mxProtoV4Fifo.add_cnt == 3) {  
            if (dat >= 2 && dat <= 250) {
                mxProtoV4Fifo.buff[mxProtoV4Fifo.add_cnt++] = dat;
                mxProtoV4Fifo.left_cnt = mxProtoV4Fifo.buff[3];
                datalong = mxProtoV4Fifo.left_cnt;
            } else {
                mxProtoV4Fifo.add_cnt = 0;
            }
        }
    }
}