As you can see from the s120 thread I finally managed to dump a firmware and I'd like to experiment a bit.
I am working on the first 16M of the 64M dump and I am a little unsure on the new "best practices"
what is the preferred toolchain? gcc464?
You'll need something that can output ARM and Thumb-2 code for ARMv7. The CPU seems to know both instruction sets, the firmware is mostly Thumb-2, there is some thunk code that has ARM instructions.
The CHDK build makefiles/scripts will have to be altered more or less. Since copied fw code will be thumb-2, probably the whole CHDK should be compiled as thumb-2.
If correct support of this CPU family requires gcc 4.8+, even more parts of the CHDK tools will have to be rewritten due to the no longer available arm-elf ABI (I expect incompatibilities with arm-none-eabi)...
(seeing srsa4c new thumb2 disasm script)
You only need a recent binutils with ARM support for that.
edit: my strategy is to copy the s110 code, replace the reset code with the new one and then the first part of the new boot....suggestions? dancing bits?
Yeah, you'll likely still need dancing bits. You can use an s110 disassembly to help with locating the needed firmware functions. However, don't expect that you'll be able to get a usable CHDK build right away.
Oh, and you may want to dump a few MB of RAM too, the kernel is IMHO still located in RAM.
If you're serious with continuing, I'd suggest creating an S120 thread, so SX280 owners won't get the false impression.