For exposure time, the minimum and maximum are usually specified as a number of row periods. For example, a certain sensor can have the following specification:

• Minimum exposure time: 6 row periods
• Maximum exposure time: (frame length – 30) row periods

Using resolution 2592 × 1944 as an example, the frame length is 1944 rows plus vertical blanking. Assuming the vertical blanking is 184, the frame length is 2128 rows. Therefore, the maximum exposure time is 2128 – 30 = 2098 row periods. Check the sensor driver and make sure the exposure time is written to the register according to the data sheet.

Since the DCC live tuning tool displays the exposure time in micro seconds, the preferred practice is to set the exposure time in micro seconds for 2A and perform a mapping between 2A and the sensor driver. The mapping depends on frame size and frame rate. For example, for 2592 × 1944 resolution and 60 fps, the minimum and maximum exposure time can be set as below in function get_<sensor>_ae_dyn_params():

p_ae_dynPrms->exposureTimeRange[count].min = 47;  /* 6*16.67/2128*1000 micro sec */
p_ae_dynPrms->exposureTimeRange[count].max = 16435; /* (2128-30)*16.67/2128*1000 micro sec */

Accordingly, the mapping from micro seconds to number of row periods (which is passed to the sensor driver) is provided in function gst_tiovx_isp_map_2A_values():

*exposure_time_mapped = (int) ((double)exposure_time * 2128 * 60 / 1000000 + 0.5);