collapseos/recipes/rc2014/eeprom

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
• stage3.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.

Using the at28 driver

The AT28 driver is at drv/at28.fs and is a pure forth source file so it's rather easy to set up from the base Stage 3 binary:

cat ../stage3.bin ../pre.fs ../../../drv/at28.fs ../run.fs > os.bin
../../../emul/hw/rc2014/classic os.bin

Writing contents to the AT28

The driver provides AT28! which can be plugged in adev's A!*.

It's not in the Stage 3 binary, but because it's a small piece of Forth code, let's just run its definition code:

cat ../../../drv/at28.fs | ./stripfc | ./exec <tty device>

Then, 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...