2a55bfd375
We use zasm's ability to use labels in .equ directive. We didn't do it before because for a while, we were in between scas and zasm (scas was used in automated tests) so we needed to use the lowest common denominator: zasm doesn't have macros and scas can't use labels in .equ directives. This forced us to add this layer of indirection. But now that we are completely cut from scas' dependency, we can use this nice zasm's ability. |
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| .. | ||
| eeprom | ||
| ps2 | ||
| sdcard | ||
| zasm | ||
| glue.asm | ||
| Makefile | ||
| README.md | ||
RC2014
The RC2014 is a nice and minimal z80 system that has the advantage of being available in an assembly kit. Assembling it yourself involves quite a bit of soldering due to the bus system. However, one very nice upside of that bus system is that each component is isolated and simple.
The machine used in this recipe is the "Classic" RC2014 with an 8k ROM module , 32k of RAM, a 7.3728Mhz clock and a serial I/O.
The ROM module being supplied in the assembly kit is an EPROM, not EEPROM, so you can't install Collapse OS on it. You'll have to supply your own.
There are many options around to boot arbitrary sources. What was used in this recipe was a AT28C64B EEPROM module. I chose it because it's compatible with the 8k ROM module which is very convenient. If you do the same, however, don't forget to set the A14 jumper to high because what is the A14 pin on the AT27 ROM module is the WE pin on the AT28! Setting the jumper high will keep is disabled.
Related recipes
This recipe is for installing a minimal Collapse OS system on the RC2014. There are other recipes related to the RC2014:
- Writing to a AT28 from Collapse OS
- Accessing a MicroSD card
- Assembling binaries
- Interfacing a PS/2 keyboard
Recipe
The goal is to have the shell running and accessible through the Serial I/O.
You'll need specialized tools to write data to the AT28 EEPROM. There seems to be many devices around made to write in flash and EEPROM modules, but being in a "understand everything" mindset, I built my own. This is the device I use in this recipe.
Gathering parts
- zasm
- romwrite and its specified dependencies
- GNU screen
- A FTDI-to-TTL cable to connect to the Serial I/O module of the RC2014
Write glue.asm
This is what your glue code would look like.
The platform.inc include is there to load all platform-specific constants
(such as RAMSTART and RAMEND).
Then come the reset vectors. If course, we have our first jump to our main init
routine, and then we have a jump to the interrupt handler defined in acia.asm.
We need to plug this one in so that we can receive characters from the ACIA.
Then comes the usual di to aoid interrupts during init, and stack setup.
We set interrupt mode to 1 because that's what acia.asm is written around.
Then, we init ACIA, shell, enable interrupt and give control of the main loop
to shell.asm.
What comes below is actual code include from parts we want to include in our
OS. As you can see, we need to tell each module where to put their variables.
See parts/README.md for details.
You can also see from the SHELL_GETC and SHELL_PUTC macros that the shell
is decoupled from the ACIA and can get its IO from anything. See
parts/README.md for details.
Build the image
We only have the shell to build, so it's rather straightforward:
zasm < glue.asm > rom.bin
Write to the ROM
Plug your romwrite atmega328 to your computer and identify the tty bound to it.
In my case (arduino uno), it's /dev/ttyACM0. Then:
screen /dev/ttyACM0 9600
CTRL-A + ":quit"
cat rom.bin | pv -L 10 > /dev/ttyACM0
See romwrite's README for details about these commands.
Running
Put the AT28 in the ROM module, don't forget to set the A14 jumper high, then
power the thing up. Connect the FTDI-to-TTL cable to the Serial I/O module and
identify the tty bound to it (in my case, /dev/ttyUSB0). Then:
screen /dev/ttyUSB0 115200
Press the reset button on the RC2014 and you should see the Collapse OS prompt!