121 lines
4.8 KiB
Markdown
121 lines
4.8 KiB
Markdown
# RC2014
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The [RC2014][rc2014] is a nice and minimal z80 system that has the advantage
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of being available in an assembly kit. Assembling it yourself involves quite a
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bit of soldering due to the bus system. However, one very nice upside of that
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bus system is that each component is isolated and simple.
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The machine used in this recipe is the "Classic" RC2014 with an 8k ROM module
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, 32k of RAM, a 7.3728Mhz clock and a serial I/O.
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The ROM module being supplied in the assembly kit is an EPROM, not EEPROM, so
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you can't install Collapse OS on it. You'll have to supply your own.
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There are many options around to boot arbitrary sources. What was used in this
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recipe was a AT28C64B EEPROM module. I chose it because it's compatible with
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the 8k ROM module which is very convenient. If you do the same, however, don't
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forget to set the A14 jumper to high because what is the A14 pin on the AT27
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ROM module is the WE pin on the AT28! Setting the jumper high will keep is
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disabled.
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## Related recipes
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This recipe is for installing a minimal Collapse OS system on the RC2014. There
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are other recipes related to the RC2014:
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* [Writing to a AT28 from Collapse OS](eeprom/README.md)
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* [Accessing a MicroSD card](sdcard/README.md)
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* [Assembling binaries](zasm/README.md)
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* [Interfacing a PS/2 keyboard](ps2/README.md)
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## Recipe
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The goal is to have the shell running and accessible through the Serial I/O.
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You'll need specialized tools to write data to the AT28 EEPROM. There seems to
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be many devices around made to write in flash and EEPROM modules, but being in
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a "understand everything" mindset, I [built my own][romwrite]. This is the
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device I use in this recipe.
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### Gathering parts
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* A "classic" RC2014 with Serial I/O
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* [Forth's stage 2 binary][stage2]
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* [romwrite][romwrite] and its specified dependencies
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* [GNU screen][screen]
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* A FTDI-to-TTL cable to connect to the Serial I/O module
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### Configure your build
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Modules used in this build are configured through the `conf.fs` file in this
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folder. There isn't much to configure, but it's there.
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### Build stage 1
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Self-bootstrapping is in Forth's DNA, which is really nice, but it makes
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cross-compiling a bit tricky. It's usually much easier to bootstrap a Forth
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from itself than trying to compile it from a foreign host.
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This makes us adopt a 2 stages strategy. A tiny core is built from a foreign
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host, and then we run that tiny core on the target machine and let it bootstrap
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itself, then write our full interpreter binary.
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We could have this recipe automate that 2 stage build process all automatically,
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but that would rob you of all your fun, right? Instead, we'll run that 2nd
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stage on the RC2014 itself!
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To build your stage 1, run `make` in this folder, this will yield `os.bin`.
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This will contain that tiny core and, appended to it, the Forth source code it
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needs to run to bootstrap itself. When it's finished bootstrapping, you will
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get a prompt to a full Forth interpreter.
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### Emulate
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The Collapse OS project includes a RC2014 emulator suitable for this image.
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You can invoke it with `make emul`. See `emul/hw/rc2014/README.md` for details.
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### Write to the ROM
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Plug your romwrite atmega328 to your computer and identify the tty bound to it.
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In my case (arduino uno), it's `/dev/ttyACM0`. Then:
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screen /dev/ttyACM0 9600
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CTRL-A + ":quit"
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cat rom.bin | pv -L 10 > /dev/ttyACM0
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See romwrite's README for details about these commands.
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Note that this method is slow and clunky, but before long, you won't be using
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it anymore. Writing to an EEPROM is much easier and faster from a RC2014
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running Collapse OS, so once you have that first Collapse OS ROM, you'll be
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much better equipped for further toying around (unless, of course, you already
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had tools to write to EEPROM. In which case, you'll be ignoring this section
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altogether).
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### Running
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Put the AT28 in the ROM module, don't forget to set the A14 jumper high, then
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power the thing up. Connect the FTDI-to-TTL cable to the Serial I/O module and
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identify the tty bound to it (in my case, `/dev/ttyUSB0`). Then:
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screen /dev/ttyUSB0 115200
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Press the reset button on the RC2014 to have Forth begin its bootstrap process.
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Note that it has to build more than half of itself from source. It takes about
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30 seconds to complete.
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Once bootstrapping is done you should see the Collapse OS prompt. That's a full
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Forth interpreter. You can have fun right now.
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However, that long boot time is kinda annoying. Moreover, that bootstrap code
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being in source form takes precious space from our 8K ROM. We already have our
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compiled dictionary in memory. All we need to have a instant-booting Forth is
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to combine our stage1 with our compiled dict in memory, after some relinking.
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TODO: write this, do this.
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[rc2014]: https://rc2014.co.uk
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[romwrite]: https://github.com/hsoft/romwrite
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[stage2]: ../../emul
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[screen]: https://www.gnu.org/software/screen/
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