133 lines
3.9 KiB
Markdown
133 lines
3.9 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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## Goal
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Have the shell running and accessible through the Serial I/O.
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## Pre-collapse
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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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* Collapse OS parts in `/path/to/parts`
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* [scas][scas]
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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 of the RC2014
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### Write main.asm
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This is what your glue code would look like:
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```
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#include "platforms/rc2014.inc"
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jr init
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.fill 0x38-$
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jp aciaInt
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init:
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di
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; setup stack
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ld hl, RAMEND
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ld sp, hl
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im 1
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call aciaInit
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call shellInit
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ei
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call shellLoop
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#include "core.asm"
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ACIA_RAMSTART .equ RAMSTART
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#include "acia.asm"
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SHELL_RAMSTART .equ ACIA_RAMEND
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.define SHELL_GETC call aciaGetC
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.define SHELL_PUTC call aciaPutC
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#include "shell.asm"
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```
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The `platform.inc` include is there to load all platform-specific constants
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(such as `RAMSTART` and `RAMEND`).
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Then come the reset vectors. If course, we have our first jump to our main init
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routine, and then we have a jump to the interrupt handler defined in `acia.asm`.
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We need to plug this one in so that we can receive characters from the ACIA.
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Then comes the usual `di` to aoid interrupts during init, and stack setup.
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We set interrupt mode to 1 because that's what `acia.asm` is written around.
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Then, we init ACIA, shell, enable interrupt and give control of the main loop
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to `shell.asm`.
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What comes below is actual code include from parts we want to include in our
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OS. As you can see, we need to tell each module where to put their variables.
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See `parts/README.md` for details.
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You can also see from the `SHELL_GETC` and `SHELL_PUTC` macros that the shell
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is decoupled from the ACIA and can get its IO from anything. See
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`parts/README.md` for details.
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### Build the image
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We only have the shell to build, so it's rather straightforward:
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scas -I /path/to/parts -o rom.bin main.asm
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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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### 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 and you should see the Collapse OS prompt!
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## Post-collapse
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TODO
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[rc2014]: https://rc2014.co.uk
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[romwrite]: https://github.com/hsoft/romwrite
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[scas]: https://github.com/KnightOS/scas
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[screen]: https://www.gnu.org/software/screen/
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