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Bought an older Sigma 70-300 lens for $10, and it turns out older Sigma lenses are incompatible with newer bodies because Sigma failed at RE and didn't implement the commands old bodies *didn't* use. So let's fix that with a modchip. Need to patch cmd 0x13 into 0x12.pic.twitter.com/A16GHik4Ny
@RechipSigma is selling modchips for $30, and they used to have the attiny firmware up but took it down and tripled the prices (and nobody mirrored it). Sorry, but I'll write my own code instead, and open source it. And it'll be better than the older one that's floating around.
looks expensive
Neat FPGA, is that the one back from DSI RAM hax days or am I confusing? Anyway good stuff :3
Yep, same old. Still my logic analyzer of choice.
If you are familiar with the TX19A architecture (TMP19A43CDXBG on 600D), this bug might be patchable directly in camera software, without any wires. We've got a memory dumper for the CPU that handles lens communication (Canon calls it MPU), but never tried to reprogram it.
I thought of patching it on the camera, but it would be good to just have the lens work on any other camera too. And there's plenty of space inside for an attiny, and I needed to take it apart for cleaning anyway :-)
Wait, how are they bad at reverse-engineering? How could the older lenses (presumably released when the older cameras were the only ones?) support the newer commands when the old bodies didn't use them? How would they even know what those commands were?
There are 256 possible commands, so you try them all. This isn't rocket science: when you're trying to clone hardware, you don't just use it as intended, you try all potential undocumented commands too.
Took me a few reads to understand...so, if I got it right, the problem is they made a lens that only supported commands used by bodies available at the time, even though the original lenses at the time supported more, so they fail in newer bodies that use those more commands?
Yup. It seems Canon lenses will accept both 0x12 and 0x13 for aperture control (I don't know if there is any difference - they might be aliases). Older bodies used 0x12, newer ones 0x13. Sigma only implemented 0x12 initially.
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