海思如何修改摄像头曝光时间？（hi3516DV300）

每个主程序运行周期修改并打印曝光参数：

        ISP_EXPOSURE_ATTR_S pstExpAttr;
        ISP_DRC_ATTR_S pstDRC;
        ISP_EXP_INFO_S stExpInfo;

        HI_MPI_ISP_GetExposureAttr(0,&pstExpAttr);
        pstExpAttr.bByPass = HI_FALSE;
        pstExpAttr.enOpType = OP_TYPE_AUTO;
        // pstExpAttr.stAuto.u8Tolerance=100;
        pstExpAttr.stAuto.stAGainRange.u32Max=0x7FFFFFFF;
        pstExpAttr.stAuto.stAGainRange.u32Min=0x400;
        pstExpAttr.stAuto.stDGainRange.u32Max=0x7FFFFFFF;
        pstExpAttr.stAuto.stDGainRange.u32Min=0x400;
        pstExpAttr.stAuto.stISPDGainRange.u32Max=0x7FFFFFFF;
        pstExpAttr.stAuto.stISPDGainRange.u32Max=0x400;
        pstExpAttr.stAuto.u16EVBias=0x90;
        pstExpAttr.stAuto.stExpTimeRange.u32Min=300;
        pstExpAttr.stAuto.stExpTimeRange.u32Max=400000;
        pstExpAttr.stAuto.u8Speed = 0x80; 
        HI_MPI_ISP_SetExposureAttr(0, &pstExpAttr);

        HI_MPI_ISP_GetDRCAttr(0, &pstDRC);
        pstDRC.bEnable=HI_TRUE;
        HI_MPI_ISP_SetDRCAttr(0, &pstDRC);

        HI_MPI_ISP_QueryExposureInfo(0,&stExpInfo);
        printf("Sensor exposure time: %dus\n",stExpInfo.u32ExpTime);
        printf("Analog Gain: %d\n",stExpInfo.u32AGain);
        printf("Digital Gain: %d\n",stExpInfo.u32DGain);
        printf("ISP Gain: %d\n",stExpInfo.u32ISPDGain);
        printf("Exposure: %d\n",stExpInfo.u32Exposure);
        printf("Average Luminance: %d\n",stExpInfo.u8AveLum);
        printf("Hist error: %d\n",stExpInfo.s16HistError);
        stExpInfo.bExposureIsMAX ? printf("Exposure is MAX!\n") : 
        printf("Exposure is NOT MAX!\n");

输出结果：
Sensor exposure time: 2730us
Analog Gain: 9667
Digital Gain: 1024
ISP Gain: 1088
Exposure: 483350
Average Luminance: 0
Hist error: 40
Exposure is MAX!
似乎没办法修改摄像头曝光参数，是AE没生效，还是AE会自动调整为默认值？
请问是逻辑问题，还是设置参数的时机不对，是要在初始化vi之后设置或绑定vpss到VDEC后，还是在已经获取视频流数据的时候调用get-set也可以修改？小白疑惑，希望大佬指点（抱拳）谢谢！
包括使用手动模式也是一样的输出，修改不到曝光时间：

        pstExpAttr.enOpType = OP_TYPE_MANUAL; 
        pstExpAttr.stManual.enAGainOpType = OP_TYPE_MANUAL;
        pstExpAttr.stManual.enDGainOpType = OP_TYPE_MANUAL;
        pstExpAttr.stManual.enISPDGainOpType = OP_TYPE_MANUAL;