Corvette CCM Reverse Engineering Anyone?

[spfautsch]

... clearly it knows exactly what your odometer is, and yet the odometer register is off by ~6 miles. So how does it both not know your precise odometer reading and also display your precise odometer reading?

Actually it wasn't off by 6, it was off by 8. Yours had 01 in the first byte which I assumed was the lsb. I'm still not sure what this signifies, but apparently the low 4 bits aren't stored in the triplet structure.

$b5fe: 00 00 01 1f ff 4d ff ff ff ff

I assumed this was to be decoded to 0x1f4d1 but I think it should have been decoded to 0x1f4d0.

It just so happened that mine is as such:

$b5fe: 00 00 01 2b ff 8d ff ff ff ff > 0x2b8d1 = 178385 which happened to be what it reads exactly

But the salvage unit that reads 2675 in-car has:

$b5fe: 00 00 00 00 a7 00 00 00 00 00 > 0x0a70 = 2672

There's another 3 miles stored on it somewhere. Yours has 8, mine 1. I just have to figure out what units they're storing it in because it's not entirely obvious.

There is some empty pad bytes before $b600, since too small to fit code there. on 94 ccm it is alillte more empty space there. It can be used for patching for sure.

If we can dump the eprom and write some patch, at least we will be able to test mode 5 without worrying about aa response. I looked at the dump and it seems there is no checksums applied.

I think you're incorrectly assuming there's any executable code stored in whatever eeprom(s) there are on this thing. I'd wager the title to my car the program code is all in the uveprom. I'm not in any hurry to desolder it and dump. But I will if there's absolutely no other way to confirm where the different memory regions are stored physically.

If you managed to fix the car, what shall we do next. Reverse the aldl protocol and try some custom modes to write data to ccm, since there is already 2 subroutines in the aldl code that writes data to eeprom. Or the ultimate goal, change mileage.

The ultimate goal would be to reprogram these completely with open source tools.