Editing Splash Screen on V26-09a Beta

navman · #10 02-24-2006, 05:06 AM

Quote:

Originally Posted by Seedar

Hi, I believe you will need to address two issues if its anything like the embedded software I have been involved with in the past.

1. If the gif is a different size than the original you will probably get errors as the linked image probably requires different modules all at previously assigned places - set at image link time. I think you would need to make the image identical size to get around this with the same byte alignment also.

2. There is no doubt a checksum across the whole image to ensure the Nav hardware doesn't start running corrupt s/w and therefore die in a nasty way. This I dont think you can get around other than to work out how the checksum is done. Presumably on the other thread where some mods were done this has been solved (?)

Good luck !

cheers,
Seedar.

Hi Seedar,

This has been covered already. When people first started replacing GIF images, I had exactly the same thoughts.. that there had to be a checksum, and indeed there is.

The "navboot" file, which is the one being modified is developed for an operating system called OS9000, and the "navboot" file is made up of modules, some of which are images, some of which are files.. In OS9000 these are all lumped together in one large file.

Each module had a header, module length, type, name, and finally at the end of the module a 24-bit checksum.

Eariler in these posts you'll find a GIFExtracter and replacer. This program locates the image modules in the "navboot" file. When using this program you'll notice that the main image module is 133Kb in size, even though the image stored in the module is only 4Kb in size. The GIF in this module can be replaced by one up to that size, using the program, and the checksum is recalculated, ensuring that the sat nav computer correctly loads the software..

So you're completely correct, but it's all been done already..

NavMan