Is there any way you could make a firmware blinker for the SX200?
Since I do not have a SX200, I cannot do anything directly... If there is some interest (let me know), I can publish a small howto based on the D10. Since it looks it has common points with the SX200, it may be useful.
Anyway, my blinker is quite a hack, and only works on linux (since I use python's alsa module), but it has the advantage that it can be easily adapted...
I don't know how much documentation is available on this, but I think it is always useful to document the special things you've done so others don't have to reinvent everything.
One thing you could do is try the dumper I made for the D10 and see if you can get that to work. If it won't work it might indicate that WriteSDCard is no longer suitable for dumping (e.g. because it depends on something that isn't initialised yet). Another possibility is that the first parameter has to be something different.
one more idea about dumping:
it would be nice to find out IO addresses of SD card controller of recent cameras and compare them.
if these addresses are the same it would be worth to make low-level driver which would make all the work with sector reading/writing.
adding some free FAT system driver would not take long...
This is something that crossed my mind as well. A very quick (and shallow) look shows
0xCXXXXXXX addresses that are the same and
0x4XXXXXXX addresses that are not. The latter might be not be a problem if it is something you have to pass through via the static addresses first.