mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-14 14:48:08 +11:00
94 lines
3.9 KiB
Markdown
94 lines
3.9 KiB
Markdown
# Writing to a AT28 from Collapse OS
|
|
|
|
## Goal
|
|
|
|
Write in an AT28 EEPROM from within Collapse OS so that you can have it update
|
|
itself.
|
|
|
|
## Gathering parts
|
|
|
|
* A RC2014 Classic
|
|
* `stage2.bin` from the base recipe
|
|
* An extra AT28C64B
|
|
* 1x 40106 inverter gates
|
|
* Proto board, RC2014 header pins, wires, IC sockets, etc.
|
|
|
|
## Building the EEPROM holder
|
|
|
|
The AT28 is SRAM compatible so you could use a RAM module for it. However,
|
|
there is only one RAM module with the Classic version of the RC2014 and we
|
|
need it to run Collapse OS.
|
|
|
|
You could probably use the 64K RAM module for this purpose, but I don't have one
|
|
and I haven't tried it. For this recipe, I built my own module which is the same
|
|
as the regular ROM module but with `WR` wired and geared for address range
|
|
`0x2000-0x3fff`.
|
|
|
|
If you're tempted by the idea of hacking your existing RC2014 ROM module by
|
|
wiring `WR` and write directly to the range `0x0000-0x1fff` while running it,
|
|
be aware that it's not that easy. I was also tempted by this idea, tried it,
|
|
but on bootup, it seems that some random `WR` triggers happen and it corrupts
|
|
the EEPROM contents. Theoretically, we could go around that by putting the AT28
|
|
in write protection mode, but I preferred building my own module.
|
|
|
|
I don't think you need a schematic. It's really simple.
|
|
|
|
### Assembling stage 3
|
|
|
|
Stage 2 gives you a full interpreter, but it's missing the "Addressed devices"
|
|
module and the AT28 driver. We'll need to assemble a stage 3.
|
|
|
|
When you'll have a system with function disk block system, you'll be able to
|
|
directly `LOAD` them, but for this recipe, we can't assume you have, so what
|
|
you'll have to do is to manually paste the code from the appropriate blocks.
|
|
|
|
Addressed devices are at B140. To know what you have to paste, open the loader
|
|
block (B142) and see what blocks it loads. For each of the blocks, copy/paste
|
|
the code in your interpreter.
|
|
|
|
Do the same thing with the AT28 driver (B480)
|
|
|
|
If you're doing the real thing and not using the emulator, pasting so much code
|
|
at once might freeze up the RC2014, so it is recommended that you use
|
|
`/tools/exec` that let the other side enough time to breathe.
|
|
|
|
After your pasting, you'll have a compiled dict of that code in memory. You'll
|
|
need to relocate it in the same way you did for stage 2, but instead of using
|
|
`RLCORE`, which is a convenience word hardcoded for stage 1, we'll parametrize
|
|
`RLDICT`, the word doing the real work.
|
|
|
|
`RLDICT` takes 2 arguments, `target` and `offset`. `target` is the first word
|
|
of your relocated dict. In our case, it's going to be `' ADEVMEM+`. `offset` is
|
|
the offset we'll apply to every eligible word references in our dict. In our
|
|
case, that offset is the offset of the *beginning* of the `ADEVMEM+` entry (that
|
|
is, `' ADEVMEM+ WORD(` minus the offset of the last word (which should be a hook
|
|
word) in the ROM binary.
|
|
|
|
That offset can be conveniently fetched from code because it is the value of
|
|
the `LATEST` constant in stable ABI, which is at offset `0x08`. Therefore, our
|
|
offset value is:
|
|
|
|
' ADEVMEM+ WORD( 0x08 @ -
|
|
|
|
You can now run `RLDICT` and proceed with concatenation (and manual adjustments
|
|
of course) as you did with stage 2. Don't forget to adjust `run.fs` so that it
|
|
runs `ADEV$`.
|
|
|
|
## Writing contents to the AT28
|
|
|
|
The driver provides `AT28!` which can be plugged in adev's `A!*`.
|
|
|
|
First, upload your binary to some place in memory, for example `a000`. To do so,
|
|
run this from your modern computer:
|
|
|
|
./upload <tty device> a000 <filename>
|
|
|
|
Then, activate `AT28!` with `' AT28! A!* !` and then run
|
|
`0xa000 0x2000 <size-of-bin> AMOVE`. `AT28!` checks every myte for integrity,
|
|
so it there's no error, you should be fine. Your content is now on the EEPROM!
|
|
|
|
Why not upload content directly to `0x2000` after having activated `AT28!`?
|
|
Technically, you could. It was my first idea too. However, at the time of this
|
|
writing, I always get weird mismatch errors about halfway through. Maybe that
|
|
the ACIA interrupt does something wrong...
|