collapseos/recipes/rc2014/selfhost

Assembling Collapse OS from within it

This is where we tie lose ends, complete the circle, loop the loop: we assemble a new Collapse OS entirely from within Collapse OS and write it to EEPROM, either for another RC2014 or for an OS upgrade.

Gathering parts

• stage3 from sdcard recipe. If you want to write to EEPROM as the final step, you'll need a hybrid stage3 that also includes stuff from the eeprom recipe.

Building stage 1

Build Collapse OS' stage 1 from within Collapse OS is very similar to how we do it from the makefile. If you take the time to look at the base recipe Makefile, you'll see cat xcomp.fs | $(STAGE2). That's the thing. Open xcomp.fs in a text editor and take a look at it.

To assemble stage 1 from RC2014, all you need to do is to type those commands in the same order, and replace the H@ 256 /MOD 2 PC! 2 PC! lines with H@ .X. Those commands will inform you of the begin/end offsets of the assembled binary.

I'm not going to explain in detail what each command do, but only give you an overview of what is happening. You are encouraged to read the in-system documentation for more information.

The first part is configuration of your new system. When RAM starts, where RSP starts, what ports to use for what device, etc. These configuration declarations are expected in the boot code and driver code.

Then, we load the Z80 assembler and the cross compiler (xcomp for short), which we'll of course need for the task ahead.

Then come xcomp overrides, which are needed for xcomp to be effective.

At this point, we're about to begin spitting binary content, so we want to know where we're at. That's why you'll need to type H@ .X and write down the result. That's the starting offset.

Then, we assemble the boot binary, drivers' native words, then inner core, close the binary with a hook word. We're finished with cross-compiling.

We're at the offset that will be CURRENT on boot, so we update LATEST.

Then, we spit the source code that will be interpreted by stage 1 on boot so that it bootstraps itself to a full interpreter. Not all units are there because they don't fit in 8K, but they're sufficient for our needs. We also need the linker so that we can relink ourselves to stage 2.

Finally, we have initialization code, then a spit of the ending offset.

Go ahead, run that. However, one thing you should know is that because the SD card driver is a bit slow, some of these commands take a long time. Multiple minutes. Be patient.

Once all your commands are run and that you have your begin/end offset (write them down somewhere), you're at the same point as you were after the make part of the base recipe. The contents between your start and end offset is the exact same as the contents of stage1.bin when you run make. Continue your deployment from there.

Good luck!

What to do on SDerr?

If you get SDerr in the middle of a LOAD operation, something went wrong with the SD card. The bad news is that it left your xcomp operation in an inconsistent state. If your at the beginning of it, it's easier to restart it entirely.

If you're towards the end, you might want to repair it. To do so, you'll have to bring your XCURRENT and HERE values to where they were before the LOAD operation. You could have thought ahead and printed them before the LOAD, but if you didn't, you'll just have to dig in your memory with DUMP.

You're looking at the offset of the last wordref of the previous LOAD operation. That offset is going in XCURRENT. Then, you're looking at the end of that word. That offset goes in HERE. Once you've done that, relaunch your LOAD.

Verifying

You can use /tools/memdump to dump the memory between your begin/end offsets so that you can compare against your reference stage 1. Before you do, you have to take yourself out of xcomp mode. First, run XCOFF to go back to your regular dict. Then, run FORGET CODE to undo the xcomp overrides you've added before. That will rewind HERE. You don't want that. Put HERE back to after your ending offset so that you don't overwrite your binary.

Then, you can run /tools/memdump.