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54 lines
1.7 KiB
Markdown
54 lines
1.7 KiB
Markdown
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# Famicom/NES programming guide
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## Program lifecycle
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The default Famicom vectors are defined as following:
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* on reset, the predefined `on_reset` routine is called, which in turn calls `main`.
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The `main` routine is not allowed to return, or the program will crash.
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* on NMI, the default interrupt handler calls the `nmi` routine.
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It should not be defined as `interrupt`, the handler is, so your routine shouldn't.
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* on IRA, the default interrupt handler calls the `irq` routine.
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It should not be defined as `interrupt`, the handler is, so your routine shouldn't.
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The minimal Famicom program thus looks like this:
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void main() {
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// initialize things
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while(true) { }
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}
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void irq() {
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// do things
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}
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void nmi() {
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// do things
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}
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## Mappers
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To use a mapper of your choice, create a new `.ini` file with the definitions you need.
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The most important ones are `[output]format` and `[allocation]segments`.
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You should define at least three segments:
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* `default` – from $200 to $7FF, it will represent the physical RAM of the console.
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* `chrrom` (sample name) – from $0000 to $3FFF, it will represent the CHRROM (if you need more).
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* `prgrom` (sample name) – from either $8000 or $C000 to $FFFF, it will contain the code of your program.
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You should set the `default_code_segment` to the segment that contains the $FFxx addresses.
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If your mapper supports it, you can add more CHRROM or PRGROM segments,
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just specify them correctly in the `[output]format` tag.
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The `[output]format` tag should contain a valid iNES header of the mapper of your choice and then all the segments in proper order.
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See [the NesDev wiki](https://wiki.nesdev.com/w/index.php/INES) for more info about the iNES file format.
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