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https://github.com/rejunity/zx-racing-the-beam
ZX Spectrum 48/128 "Racing the Beam"
https://github.com/rejunity/zx-racing-the-beam
cycle-accurate demoscene z80asm zx-spectrum
Last synced: about 1 month ago
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ZX Spectrum 48/128 "Racing the Beam"
- Host: GitHub
- URL: https://github.com/rejunity/zx-racing-the-beam
- Owner: rejunity
- License: mit
- Created: 2022-05-31T11:05:20.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2023-10-25T21:10:12.000Z (about 1 year ago)
- Last Synced: 2023-10-26T19:28:02.465Z (about 1 year ago)
- Topics: cycle-accurate, demoscene, z80asm, zx-spectrum
- Language: HTML
- Homepage:
- Size: 4.34 MB
- Stars: 0
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
ZX Spectrum 48/128 "Racing the Beam" Experiments
=====
This repo contains set of experiments for **racing the beam** and **opening the border** on ZX Spectrum 48K.
- *racing the beam* - is the besis of multicolour effects that defy 8x8 color attributes,
- *opening the border* - allows to draw outside of the normal video memory area.
Both techniques require precise cycle timing which is complicated on ZX Spectrum 48/128K due to [memory contention](https://sinclair.wiki.zxnet.co.uk/wiki/Contended_memory).
## Prerequistes and tools
Tools for Mac OSX are included directly in the repository and should not require any additional installation. (**HELP NEEDED**: *Setup for Windows and Unix!*)
- Emulator: [Fuse](https://fuse-emulator.sourceforge.net), [Fuse for Mac OSX](https://fuse-for-macosx.sourceforge.io)
- Assembler: [zmac](http://48k.ca/zmac.html)
# What next?
First run `screen_timing` example that demonstrates exact frame timing and how to draw on the border at a particular position.
Executing `make screen_timing` will compile `screen_timing.asm` file, build `screen_timing.tap` tape file and execute the emulator:
```make screen_timing```
Look at [screen_timing.asm](./screen_timing.asm) source code. It will explain frame timing for ZX Spectrum 48K and demonstrate how to catch TV beam at a desired position.
Next look at [interrupt_mode2.asm](./interrupt_mode2.asm). It provides predictable frame timing and explains at which cycle exactly frame starts.
Nothing particularly interesting happens visually just border is changing every N frames. Look at the code instead.
```make interrupt_mode2```
Next run `checkers` example that draws static image on the border:
```make checkers```
Finally look at `checkers_hscroll.asm` which willl draw animated checkerboard across the whole screen including the border.
```make checkers_hscroll```
This code races the beam and deals with [memory contention](https://sinclair.wiki.zxnet.co.uk/wiki/Contended_memory).
(**HELP NEEDED**: *Update code to run with 128K timing*)
See, if you could re-implement it with the less code or make it more readable?
### Setting up Build & Run in Sublime Text
1) Open your **Sublime Text** editor and chose Tools ▶ Build System ▶ New Build System…
2) Copy contents of the [ZXasm.sublime-build](ZXasm.sublime-build) into newly create sublime-build script, save with `ZXasm.sublime-build` name.
3) Pick any `.asm` file in the project, chose Tools ▶ Build System and specify `ZXasm`.
Now you can use Command+B (or Ctrl+B) to build & launch emulator!
For more information see [Sublime build system docs](https://www.sublimetext.com/docs/build_systems.html)
### Adding new .asm file
1) Create new `my_new_experiment.asm`
2) Add to [Makefile](Makefile): `TAPES+=my_new_experiment.tap`
3) Now you can use:
```make my_new_experiment```
## TODO
- Setup for Windows and Unix!
- Move generated and temporary files into /output folder
- Port `checkers.asm` and `checkers_hscroll.asm` to work on 128K/+2/+2A/+3, currently only 48K is supported. Each model of Spectrum unfortunately has slightly different timing :(
- Measure and update T cycles timings in `interrupt_mode2.asm` by running on 128K/+2/+2A/+3 emulated machines.
- Implement 64x48 multicolour by flipping between screen pages on 128K.
- AY at 200Mhz
- Investigate if custom code generator (say with Python) instead of zmac would simplify cycle exact code genereation
## Useful information
### Hardware
- ZX Spectrum 48K Hardware overview: [https://worldofspectrum.org/faq/reference/48kreference.htm](https://worldofspectrum.org/faq/reference/48kreference.htm#Hardware)
- Different Spectrum Models: https://spectrumforeveryone.com/technical/zx-spectrum-models/
- ULA types: https://spectrumforeveryone.com/technical/zx-spectrum-ula-types/
- ZX Spectrum schematics and PCB layouts: https://spectrumforeveryone.com/technical/zx-spectrum-pcb-schematics-layout/
### Timing
- ZX Spectrum 48K frame timing: https://worldofspectrum.org/faq/reference/48kreference.htm#ZXSpectrum
- It is very important to understand Memory Contention, 48K model: https://worldofspectrum.org/faq/reference/48kreference.htm#Contention
- ZX Spectrum 128K memory banks, frame and contention timing: https://worldofspectrum.org/faq/reference/128kreference.htm
- Z80 Instruction cycles, sizes and opcodes: https://spectrumforeveryone.com/technical/z80-processor-instructions/