Now this sounds pretty interesting...
I thought it did too, but now sort of lost enthusiasm. Yes, BD3916FVM pins 5 & 8
could 've been connected to DiGiC, although it's much more likely that newer cams use a whole different chip for the purpose. They sure enough use different CCD chips, which may or may not support such or similar functions. It seems that, e.g., A710 doesn't have VsubCont (what a pity, cannot call
ewavr for help)... Nice that we have at least this Ixus65 schematics. Ancient as it is, but still useful...
Now back to the subject. As
ewavr suggested above, perhaps every (significant) regulated voltage in the cam is connected to ADC for monitoring by OS. The VsubCont (if it controls a voltage at all) is not -- I didn't see a change in GetAdChValue() for any channel. I then tried to blindly write random/successive numbers to the ports -- to no avail, I only could see that same small change of live view brightness as with a legitimate call to VsubCont() (i.e. only a couple of bits of the ports are actually connected to something). I'm thus getting an impression that this voltage control (if it is a voltage control) is only for trimming purpose rather than for full-fledged regulation, and thus uninteresting for the original purpose of choking the pre-amp. Of course I may be wrong -- and hopefully I am.
The actual functioning of the code is well over my head though. Why three ports, of which one is clearly a bitmap (configuration port?) Is perhaps the writing order important? What do they control in the first place? And when will Canon, Inc. finally leak the freakin' service/hacking manual? Otherwise, meditating over the disasm doesn't often precipitate useful ideas...