The Powershot A1300 has full time auto focus. This switch on & off function is definitely in the CHDK 1/2 press of the Shutter menu. An up press of the Joystick pad turns on & off Manual focus. The other 1/2 press menus do not respond to their key presses. I think the porting process is the computer code that makes them work has to be completed yet. No 1/2 Press functions worked when I was running the A810 CHDK in my A1300. Have fun porting.
Which capture mode are you using for testing the 1/2 Press functions?
In a810, and my guess is that in a1300 too, the AFL is activated (even without CHDK) in this way:
- Put the camera in P or LIVE mode
- Press the "left/flower" button after "half pressing & holding" the shutter release button.