patch

Documentation

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.

The first format is simplt the output of "cmp -l <old_file> <new_file>", an example of which is shown below:

 862  22 200
 863 360 376
3713 377 242
3715 377 232
3716 377 114
3717 377  22
3718 377 360

The first column is the offset, expressed as a decimal number and measure from one. The second column is the current value of the offset being changed, and the third column is the value it is being changed to. The values in column 2 and three are expressed in octal!

The second format is what I have called the "neo" format. This seems to be an ad-hoc format taken from the "In case you can't wait" section of the following web page (the domain of which was used to help name the format):

"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.

Index

• func CartridgeMemory(cart *cartridge.Cartridge, patchFile string) (bool, error)

Functions

func CartridgeMemory

func CartridgeMemory(cart *cartridge.Cartridge, patchFile string) (bool, error)

CartridgeMemory applies the contents of a patch file to cartridge memory. Currently, patch file must be in the patches sub-directory of the resource path (see paths package).