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doc/bootstrap: fix inaccuracies

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This commit is contained in:
Virgil Dupras 2020-10-31 15:27:00 -04:00
parent 7001446212
commit 3a0084aa31
1 changed files with 22 additions and 18 deletions
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doc/bootstrap.txt
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@ -16,7 +16,7 @@ This binary can be separated in 5 distinct layers:
2. Arch-specific boot words (B305 for Z80)
3. Arch-independant core words (low) (B350)
4. Drivers, might contain arch-specific code
5. Arch-independant core words (high) (B380)
5. Arch-independant core words (high) (B390)
# Boot code
@ -28,9 +28,7 @@ It also of course does core initialization: set RSP/PSP, HERE
CURRENT, then call BOOT.
It also contains what we call the "stable ABI" in its first
0x100 bytes. The beginning of the dict is intertwined in this
layer because EXIT, (br), (?br) and (loop) are part of the
stable ABI.
few (<0x20) bytes.
# Boot words
@ -53,25 +51,26 @@ See B260 for details.
# Drivers
Up until now, we haven't implemented EMIT or KEY yet: those
words are defined in the "high" part of core words because we
generally need machine-specific drivers to implement (emit) and
(key).
Core words don't include (key) and (emit) implementations be-
cause that's hardware-dependant. This is where we need to load
code that implement it, as well as any other code we want to
include in the binary.
Well, now is their time to shine. We split core in two
precisely to fit drivers in there. This way, they have access
to a pretty good vocabulary and they're also give the oppor-
tunity to provide (emit) and (key).
We do it now because if we wait until the high layer of core
words is loaded, we'll have messed up immediates and ":" will
be broken. If we load our code before, we won't have access to
a wide vocabulary.
# Core words (high)
Then come EMIT, KEY and everything that depend on it, until
we have a full Forth interpreter. At the very end, we define
tricky IMMEDIATEs that, if defined earlier, would break cross
compilation.
The final layer of core words contains the BOOT word as well
as tricky immediates which, if they're defined sooner, mess
cross compilation up. Once this layer is loaded, we become
severly limited in the words we can use without messing up.
We end that with a hook words which is also where CURRENT will
be on boot.
After having loaded that last layer, we end that with a hook
word which is also where CURRENT will be on boot, which is then
followed by the initialization string (see below).
So that's the anatomy of a Collapse OS binary. How do you build
one? If your machine is already covered by a recipe, you're in
@ -110,4 +109,9 @@ part. The boot sequence is designed to interpret whatever comes
after LATEST as Forth source, and this, until it reads ASCII
EOT character (4). This is generally used for driver init.
To produce a Collapse OS binary, you run that xcomp unit and
then observe the values of "ORG @" and "H@". That will give you
the start and stop offset of your binary, which you can then
copy to your target media.
Good luck!