mirror of
https://github.com/JetSetIlly/Gopher2600.git
synced 2024-06-23 15:03:14 -04:00
69 lines
2.7 KiB
Go
69 lines
2.7 KiB
Go
// This file is part of Gopher2600.
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//
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// Gopher2600 is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// Gopher2600 is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with Gopher2600. If not, see <https://www.gnu.org/licenses/>.
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// Package patch is used to patch the contents of a cartridge. It works on
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// cartridge memory once a cartridge file has been attached. The package does
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// not implement the patching directly, rather the different cartridge mappers
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// (see cartridge package) deal with that individually.
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//
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// This package simply loads the patch instructions, interprets them and calls
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// the cartridge.Patch() function.
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//
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// The first format is simplt the output of "cmp -l <old_file> <new_file>", an
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// example of which is shown below:
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//
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// 862 22 200
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// 863 360 376
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// 3713 377 242
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// 3715 377 232
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// 3716 377 114
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// 3717 377 22
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// 3718 377 360
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//
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// The first column is the offset, expressed as a decimal number and measure
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// from one. The second column is the current value of the offset being
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// changed, and the third column is the value it is being changed to. The
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// values in column 2 and three are expressed in octal!
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//
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// The second format is what I have called the "neo" format. This seems to be
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// an ad-hoc format taken from the "In case you can't wait" section of the
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// following web page (the domain of which was used to help name the format):
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//
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// "Fixing E.T. The Extra-Terrestrial for the Atari 2600"
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//
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// http://www.neocomputer.org/projects/et/
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//
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// The following extract illustrates the format:
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//
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// -------------------------------------------
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// - E.T. is Not Green
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// -------------------------------------------
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// 17FA: FE FC F8 F8 F8
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// 1DE8: 04
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//
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// Rules:
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//
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// 1. Lines beginning with a hyphen or white space are ignored
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// 2. Offset and values are expressed in hex (case-insensitive)
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// 3. Values and offsets are separated by a colon
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// 4. Multiple values on a line are poked into consecutive offsets, starting
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// from the offset value
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//
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// Note that offsets are expressed with origin zero and have no relationship
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// to how memory is mapped inside the VCS. Imagine that the patches are being
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// applied to the cartridge file image. The cartridge mapper handles the VCS
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// memory side of things.
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package patch
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