Kakute f4 mini ardupilot4.1.3 GPS problem

good day,

I bought a brand new kakute F4 mini and flashed ardupilot 4.1.3 firmware, everything is ok except GPS. I use BN 880 GPS and connect to uart6, set baudrate to 38400, gps type to nema,also config gps via U center to this baudrate, the compass is good,but gps cannot be found. i changed the gps output to ublox,set gps type to ublox in mission planner, still no good. after i read some some post, I set the parameter GPS_DRV_OPTION=4, still no good. but when I changed GPS_AUTO_CONFIG=1, gps can be found. It seems only set GPS_AUTO_CONFIG=1, gps works.
Even set this,GPS is very difficult get 3D fix, it can float in the.map of mission planner for 5 minutes with no 3d fix, even never fix.

but when I connect BN880 to U center via FDTI, its 3d fix very quickly. so what the process and how ardupilot talk to gps, thats really get.me confused.

thanks for any suggestions.

Set your GPS to 115200 baud and set GPS_DRV_OPTIONS to 2.

38400 baud is too slow. If you do a search, you’ll find discussions about adding GPS_DRV_OPTIONS 2 and why it was necessary.

I set gps baudrate to 115200, and GPS_DRV_OPTION=2 or 4, it seems no difference. but if I set GPS_AUTO_CONFIG=0,
there is no gps in mission planner. I am still confused. why GPS_AUTO_CONFIG must be set as 1?