patch

Overview ¶

Package patch is used to patch the contents of a cartridge. It works on cartridge memory once a cartridge file has been attached. The package does not implement the patching directly, rather the different cartridge mappers (see cartridge package) deal with that individually.

This package simply loads the patch instructions, interprets them and calls the cartridge.Patch() function. Currently only one patch format is supported. This is an ad-hoc format taken from the "In case you can't wait" section of the following web page:

"Fixing E.T. The Extra-Terrestrial for the Atari 2600"

http://www.neocomputer.org/projects/et/

The following extract illustrates the format:

-------------------------------------------
- E.T. is Not Green
-------------------------------------------
17FA: FE FC F8 F8 F8
1DE8: 04

Rules:

1. Lines beginning with a hyphen or white space are ignored
2. Offset and values are expressed in hex (case-insensitive)
3. Values and offsets are separated by a colon
4. Multiple values on a line are poked into consecutive offsets, starting from the offset value

Note that offsets are expressed with origin zero and have no relationship to how memory is mapped inside the VCS. Imagine that the patches are being applied to the cartridge file image. The cartridge mapper handles the VCS memory side of things.