rc2014: update README
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Virgil Dupras
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@ -31,7 +31,6 @@ are other recipes related to the RC2014:
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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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To make things fun, we play with I/Os using RC2014's Digital I/O module.
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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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@ -40,46 +39,35 @@ device I use in this recipe.
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### Gathering parts
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* [zasm][zasm]
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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 of the RC2014
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* (Optional) RC2014's Digital I/O module
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### Write glue.asm
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### Configure your build
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[This is what your glue code would look like.](glue.asm)
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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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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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### Build stage 1
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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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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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We need to plug this one in so that we can receive characters from the ACIA.
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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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Then comes the usual `di` to aoid interrupts during init, and stack setup.
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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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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 the BASIC shell.
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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 `apps/README.md` for details.
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You can also see from the `STDIO_GETC` and `STDIO_PUTC` macros that the shell
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is decoupled from the ACIA and can get its IO from anything. See comments in
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`kernel/stdio.asm` 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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../../emul/zasm/zasm ../../kernel < glue.asm > os.bin
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Running `make` will also work.
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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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@ -105,23 +93,22 @@ 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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See documentation in `apps/basic/README.md` for details.
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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 a
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while (TODO: indicate how many minutes).
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For now, let's have some fun with the Digital I/O module. Type this:
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Once bootstrapping is done, you'll get a and you should see the Collapse OS
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prompt. That's a full Forth interpreter. You can have fun right now.
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```
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> a=0
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> 10 out 0 a
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> 20 sleep 0xffff
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> 30 a=a+1
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> 40 goto 10
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> run
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```
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However, that multi-minutes boot is kinda annoying. Moreover, that bootstrap
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code being in source form takes precious space from our 8K ROM. We already have
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our compiled dictionary in memory. All we need to have a instant-booting Forth
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is to combine our stage1 with our compiled dict in memory, after some
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relinking.
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You now have your Digital I/O lights doing a pretty dance, forever.
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TODO: write this.
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[rc2014]: https://rc2014.co.uk
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[romwrite]: https://github.com/hsoft/romwrite
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[zasm]: ../../tools/emul
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[stage2]: ../../emul
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[screen]: https://www.gnu.org/software/screen/
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