The CHDK Custom Auto ISO is enabled by default & gets active when a camera mode with Canon's AutoISO is selected...
Thinking about this further (and looking at the code)...
This is *wrong*. Not fe50s description, but the what it does. CHDK should not change the cameras behavior unless the user asks. Particularly, if someone just installs CHDK and starts using it, without explicitly turning anything on it definitely should NOT change exposure behavior. The default is changed to OFF in changesets 2052 and 2053
More ranting:
gui_osd_draw_state() has the following
if ((conf.autoiso_enable && shooting_get_iso_mode()<=0 && !(m==MODE_M || m==MODE_TV) && shooting_get_flash_mode() && (!(conf.override_disable==1 && conf.override_disable_all))) || gui_mode==GUI_MODE_OSD)
The actual auto ISO code doesn't have the same set of conditions...
if (m==MODE_M || m==MODE_TV || m==MODE_STITCH) return; //Only operate outside of M and Tv
The correct way to do this would be to make function like shooting_should_do_auto_iso() and call it in both places (but of course, the actual auto-iso logic is spread over several functions...)
Note that the osd logic will also show autoiso enabled in video modes...
Even more ranting:
the defines USE_REAL_AUTOISO and OVEREXP_COMPENSATE_OVERALL are only set for sx230. This does not seem to be due to any special characteristics of that camera. If the option is actually better, then we should use it everywhere. If it's not, then we shouldn't. If there is value in each option, then we should make it a run time option.