Please help.
In at least Snadragon 617 and perhaps other SoCs, Qualcomm provides format support for RAW camera files which is beyond the scope of the Camera1 android API. A couple enterprising coders have created a wonderful freeware app called FreeDCam which enables RAW camera support for a variety of smartphones which are not "Camera2 API capable" through a variety of innovative methods including taking advantage of native RAW support (Qualcomm), engineering mode (MediaTek), integrating 3rd party freeware for "containerizing" RAW to DNG format, etc etc.
Over time it has become evident that several smartphone vendors including ZTE and Xiaomi have made coding errors or omissions in creation of camera drivers and/or HAL libraries which cause FreeDCam to be unable to provide manual ISO support for ZTE Zmax Pro and Xiaomi redmi Note 3 which SHOULD function exactly as the manual parameter settings work for jpeg format files (the app fully supports manual exposure time, manual or fixed ISO, and manual white balancing).
According to the developers (I have no affiliation with them....I'm just a ZTE ZMAX PRO owner trying to leverage their app for RAW format photography), the reason the app does not behave properly is because smartphone OEMs have created library files which do not correctly handle setting manual exposure when file format is RAW (despite handling the same correctly when file format is JPG). From the developers perspective, OEM or hardware provider are the only entities who can find and correct the errors (again, this is a freeware app we are talking about), and the OEMs have already demonstrated that they have neither the motivation nor the capability of generating correct HAL/driver code.
So I'm contacting you the hardware provider directly to see if you can isolate the incorrect code associated with your camera hardware and either correct it or at a minimum point to the specific files that require correction (ZTE firmware has been released under GNU as is available for review/correction).
The "issue threads" for problems associated with software implementation of Snapdragon 617 hardware are available in the github repository for the freeware Freedcam app....
Xiaomi: https://github.com/troop/FreeDcam/issues/61
ZTE Zmax Pro: https://github.com/troop/FreeDcam/issues/126
Thanks for your time and attention.