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139 lines
4.9 KiB
Markdown
139 lines
4.9 KiB
Markdown
# erc
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### (Emulator of old, Retro Computers)
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---
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Erc is software that allows you to emulate computers from the days of
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yore. (The "days of yore" may be defined as the 1980s.) You may find it
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interesting if you feel nostalgia for those old machines, or if you want
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to see how those computers worked.
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Erc is also a sound you might make when feeling slightly frustrated, or
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if you were a small cat that happens to make funny sounds that aren't
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quite meows.
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## Goals
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I've long had an interest in retro computing, collecting books on the
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6502 processor in particular, and this program has been written and
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rewritten in fits and starts over several years (and in several
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languages!). Being able to emulate the Apple II, which was my childhood
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computer, has been a dream of mine for some time!
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Erc is written in C, largely because I have long loved that language,
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though I have not had much need to use it in my professional career. C
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is a somewhat cranky language, and not one that lends itself to modern
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engineering practices, so erc was partly written as a challenge to
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myself to try and elevate the language.
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In particular, it's a goal of mine to ensure that erc:
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* is written for other developers to read, especially as a reference for
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those who are interested in emulation in general and the platforms
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emulated here in particular;
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* is modular, allowing as much code reuse within the application as is
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practical;
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* is unit-testable, to the extent that C allows, and maintains a high
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level of code coverage.
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## Updates (Jan 18, 2018)
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I thought I'd write something on the state of the emulator. Here's
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what's done so far:
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* We have fully implemented the MOS 6502 processor support for the Apple
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II, and we have much of the infrastructure to emulate an Apple II
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machine in place now.
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* Memory organization is principally complete. There's a lot of memory
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in the Apple II! You have main memory, auxiliary memory,
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bank-switchable memory, read-only memory. Early on, we implemented
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memory map support for vm_segments, which is something that has
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been flexible enough to support all of the types of soft-switches
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that the Apple II has to control access to said memory (as well as
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for many other functions).
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* There's a basic disassembler in place for the 6502 support, which has
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been incredibly helpful in identifying where we have had functional
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breakdowns in terms of proper execution and bootstrapping of the
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"machine".
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* We're up to 169 tests as of the time of this writing, which is
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awesome!
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We do have a lot of stuff done for the graphics system, but there's a
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lot more to go; getting graphics and text working as intended is my next
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goal. I'm hopeful this will lead us to a point where erc is usable with
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general disk images of software.
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Some ideas for the future:
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* An assembler that could splice a program into multiple disk images
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* Commadore 64 support (which will be difficult, as I've used a
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Commadore maybe...one time? Two times?)
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## Running
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Running erc right now is a bit hazardous; not in the sense that it will
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break anything, but more in the sense that you may not know what you
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should be doing. Since it is still somewhat in flux, I won't go into too
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much detail on how you can run it; I will point you to the help
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printout, which you can see by doing this:
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```
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./erc --help
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```
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(The above assumes you have built the software in the `build` subdir,
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and are actually in that subdir.) Generally speaking, you can indicate
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what you have in one of two "disk drives", given a valid disk image for
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an Apple II (e.g. something ending in .dsk, .do, etc., and having the
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proper length for said image).
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## Compiling and installing
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This software uses CMake to build its makefiles, so if you're familiar
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with that, you should feel somewhat at home.
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If you've never compiled any C code before, you will need to install a
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few things first. If you have not done so, you should install the
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excellent [Homebrew](https://brew.sh/) if using a Mac. If you are using
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Linux, you are probably already acquainted with your local package
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manager. You will also need to have XCode installed in a Mac
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environment. You can do so through the App Store.
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The following other things you must install are given as Homebrew
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commands. If you are using Linux, I will leave the appropriate commands
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you must run as an exercise for the reader.
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```
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brew install cmake
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brew install snaipe/soft/criterion
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```
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Once all that is accomplished, you can do this:
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```
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cd build
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cmake ..
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make
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```
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This should produce an executable of the emulator, which you can install
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wherever you wish.
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## Testing
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If you're feeling a bit nosy, you can run unit tests by doing the following:
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```
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cd tests/build
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cmake ..
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make; ./erc-test
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```
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This will execute the testing build of the software, which is handled
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through [Criterion](https://github.com/Snaipe/Criterion).
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## Contributing
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Right now, I am not accepting pull requests as so much of the design of
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erc is in flux. I am happy to receive any issues you may file.
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