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# erc
### (Emulator of old, Retro Computers)
---
Erc is software that allows you to emulate computers from the days of
yore. (The "days of yore" may be defined as the 1980s.) You may find it
interesting if you feel nostalgia for those old machines, or if you want
to see how those computers worked.
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Erc is also a sound you might make when feeling slightly frustrated, or
if you were a small cat that happens to make funny sounds that aren't
quite meows.
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## Goals
I've long had an interest in retro computing, collecting books on the
6502 processor in particular, and this program has been written and
rewritten in fits and starts over several years (and in several
languages!). Being able to emulate the Apple II, which was my childhood
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,
though I have not had much need to use it in my professional career. C
is a somewhat cranky language, and not one that lends itself to modern
engineering practices, so erc was partly written as a challenge to
myself to try and elevate the language.
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In particular, it's a goal of mine to ensure that erc:
* is written for other developers to read, especially as a reference for
those who are interested in emulation in general and the platforms
emulated here in particular;
* is modular, allowing as much code reuse within the application as is
practical;
* is unit-testable, to the extent that C allows, and maintains a high
level of code coverage.
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## Updates (Jan 18, 2018)
I thought I'd write something on the state of the emulator. Here's
what's done so far:
* We have fully implemented the MOS 6502 processor support for the Apple
II, and we have much of the infrastructure to emulate an Apple II
machine in place now.
* Memory organization is principally complete. There's a lot of memory
in the Apple II! You have main memory, auxiliary memory,
bank-switchable memory, read-only memory. Early on, we implemented
memory map support for vm_segments, which is something that has
been flexible enough to support all of the types of soft-switches
that the Apple II has to control access to said memory (as well as
for many other functions).
* There's a basic disassembler in place for the 6502 support, which has
been incredibly helpful in identifying where we have had functional
breakdowns in terms of proper execution and bootstrapping of the
"machine".
* We're up to 169 tests as of the time of this writing, which is
awesome!
We do have a lot of stuff done for the graphics system, but there's a
lot more to go; getting graphics and text working as intended is my next
goal. I'm hopeful this will lead us to a point where erc is usable with
general disk images of software.
Some ideas for the future:
* An assembler that could splice a program into multiple disk images
* Commadore 64 support (which will be difficult, as I've used a
Commadore maybe...one time? Two times?)
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## Running
Running erc right now is a bit hazardous; not in the sense that it will
break anything, but more in the sense that you may not know what you
should be doing. Since it is still somewhat in flux, I won't go into too
much detail on how you can run it; I will point you to the help
printout, which you can see by doing this:
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```
./erc --help
```
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(The above assumes you have built the software in the `build` subdir,
and are actually in that subdir.) Generally speaking, you can indicate
what you have in one of two "disk drives", given a valid disk image for
an Apple II (e.g. something ending in .dsk, .do, etc., and having the
proper length for said image).
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## Compiling and installing
This software uses CMake to build its makefiles, so if you're familiar
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
few things first. If you have not done so, you should install the
excellent [Homebrew](https://brew.sh/) if using a Mac. If you are using
Linux, you are probably already acquainted with your local package
manager. You will also need to have XCode installed in a Mac
environment. You can do so through the App Store.
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The following other things you must install are given as Homebrew
commands. If you are using Linux, I will leave the appropriate commands
you must run as an exercise for the reader.
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```
brew install cmake
brew install snaipe/soft/criterion
```
Once all that is accomplished, you can do this:
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```
cd build
cmake ..
make
```
This should produce an executable of the emulator, which you can install
wherever you wish.
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## Testing
If you're feeling a bit nosy, you can run unit tests by doing the following:
```
cd tests/build
cmake ..
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make; ./erc-test
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```
This will execute the testing build of the software, which is handled
through [Criterion](https://github.com/Snaipe/Criterion).
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## Contributing
Right now, I am not accepting pull requests as so much of the design of
erc is in flux. I am happy to receive any issues you may file.