It's been a long while since I visited this part of the code and it
has become a bit messy after having gone through all evolutions of
the core code.

It is now simpler, more compact.

Previously, these words would be ascii emitters, but seldom used
except for the SPC emitter. However, I would often end up hardcoding
these constants. With useless emitters removed and ASCII constants
added, we have a more usable system.

Also, fix broken test harness.

It doesn't require emitting words anymore. The rename to NL> is
linked to the upcoming commit.

Also, remove extraneous uses of it. In the rdln routine, we would
spit a new line after each line input, but that NL was spurious:
we already spit the newline we receive as it is typed.

It's a bit wasteful to spit full NLs.

The textual introduction of blk 0 was there when documentation was
inside the blkfs. Now that it's outside it, it serves no purpose:
you're expected to have read the documentation already before seeing
blk 0.

... and rename it to KEY?. Then, add KEY from KEY? for its blocking
version.

I need this for an upcoming Remote Shell feature. If a Collapse OS
system remotely controls another shell, it needs to be able to poll
both the remote system and the local keyboard at the same time. A
blocking KEY is incompatible with this.

In some places, the polling mechanism doesn't make sense, so this
new KEY? always returns a character. In some places, I just haven't
implemented the mechanism yet, so I kept the old blocking code and
added a "always 1" flag as a temporary shim.

I have probably broken something, but in emulators, Collapse OS runs
fine. It's an important reminder of what will be lost with the new
"dogfooding" approach (see recent mailing list message): without
emulators, it's much harder to to sweeping changes like this without
breaking stuff.

It's fine, I don't expect many more of these core changes to the
system. It's nearly feature-complete.

I forgot to do so when I updated FLUSH.

The buffer's implementation wasn't buying us much in exchange for its
complexity. A modern machine was still too fast for it (copy/pasting
text from a modern machine would send bytes too fast for the RC2014)
and in the (theoretical so far) case of COS-to-COS communication, the
buffer didn't help in cases where the baud rate was faster than the
processing of each byte received (for example, if the byte was written
directly to EEPROM).

I'm scrapping it and, instead, use the RTS flag to signal the other
side when we're ready to receive a new byte.

Also, implement driver for channel B in SIO. I will need it to talk
to my TRS-80 4P.

No more relying on the TRS-DOS driver!

Previously, inserting at a position that had null chars before it
would result in a block that wouldn't properly display with LIST.

In emulation, emitting is near-immediate. On a real machine, it's
often not-so-near-immediate. These little things help usability.

Again, this commit was meta-developed!

Uninitialized blocks often contains garbage, and emitting it on
the TRS-80 4P results in serious visual glitches.

Loading the grid subsystem on top of the TRS-80 driver, which is
an interface to its ROM BIOS, would be counter-productive because
the BIOS already has the concept of cursor.

However, VE needs the Grid interface, so we implement a shim for it.

Again, all this work (and the re-assembly that it entails) has been
done from within Collapse OS on the TRS-80!

On a TRS-80 4P, spitting control chars, in addition to being
visually distasteful, generated a bug where the blinking cursor
would disappear, making using VE much, much harder.

I had a hard time reproducing the bug: you don't trigger it by
simply spitting control chars, it had to be a specific number of
them in a specific order. I didn't identify the sequence, but I
know that "bufp" triggered it.

This commit was written on a TRS-80 4P and downloaded from my work
floppies!

When developing from a Collapse OS environment, it's necessary to
be able to download blocks from it.

So far, I've been using this tool on remotes that had no control
character handling, but it doesn't work on a TRS-80 4P remote.

Much slower, but at least it works.

Later, I'll try to put some order in this so that we use the fast
lane when possible.

This optimisation appears to make the upload process unreliable in
some cases. I can't appear to reliably upload to my TRS-80 with this
version. I prefer reliability than speed...

When I get bitten by it myself, it's because it's clearly
underdocumented!

We couldn't get a tilde!

I've tested that it works in emulation. The only test left is the
real deal my a Sega Master System.

A ~C! override can, if it wants, go put an error code in there,
which ~AT28 does.

This way, after a copy or xcomp process directly to EEPROM, one
can verify whether all bytes were successfully written by checking
whether "~C!ERR C@" is zero.

They're only used once.

Also, turn AT28! and AT28, into ~AT28, pluggable into ~C!.

~AT28 doesn't check for mismatches. It was too complicated to turn
a mismatch into a compiled word we would jump to next. Data
integrity has to be checked through another path.

Also, remove MOVEW. Without indirect memory access, this word
doesn't make sense. Some AVR-specific words will have to be
defined.

This will facilitate the development of a solution for
cross-compiling directly to EEPROM.

I got bitten again, I've over-designed my solution. The last time
it happened, it was that memory mapping thing I was wanting to add.

The indirect memory access feature I was adding was to solve a
specific problem: Allow Collapse OS to cross-compile directly on a
AT28 EEPROM.

It began well. As long as we were staying in the assembler realm,
things were looking good. However, when we got into the xcomp realm
(B260), things became ugly, and I had to creep up indirection where
I didn't want to.

All of this because I wanted to solve my initial problem in a
slightly more generalized way. The broad idea was that these indirect
memory access could allow xcomp into a broad kind of memory-like
devices.

This idea broke on the "@" part of the equation. If I want
indirections to be two-way and allow xcomp to work properly, I have
to add this indirection to FIND (and possibly others) and this just
isn't practical or elegant.

So, I'm taking a step back and accepting that the solution I design
for now is exclusively for the AT28. What I'm thinking is to add a
low-level hook for memory writing, at the assembly level.

Splitting a word into MSB/LSB pairs happens often and is worth, I
think, native words. Also, I'm going to need it in the upcoming
commits.

This allows SMS xcomp to use ALLOT0 instead of ZFILL,

Also, rename "Addressed devices" to "Indirect memory access".

I do this because I need to add indirect versions of !, @ and ,
to allow boostrapping directly to EEPROM and that A,, thing I've
added to assemblers felt like really bad names.

With this change, I'd like to generalize the use of the * suffix
for aliases.

This word, suitable to plug to A, , increases HERE before doing its
verification to minimize waiting time: While we increase HERE, the
AT28 has the time to do its programming, and thus we'll need to idle
for less time afterwards.

Also, made the mismatch check silently ignore MSB. Previously, writing
a value larger than 0xff with AT28! would always result in a mismatch.

So far, only the first 400 sectors of the disk image are accessible.

TODO: add keybindings to swap floppies on the emulated machine.

Not complete yet, but has @KEY and @DSP, enough to get prompt.

During the recipe overhaul, I forgot to carry PS/2 schematics over.
Also, the recipe should go in hw/z80 because it's specific to Z80.

Add an example, which I think helps a lot to grasp the idea.

Also, improve comments in Z80 boot code.

This brings us a bit closer to TYPE from Forth 2012. I don't think
I'll add TYPE (sig "addr len") anytime soon because there is few
use cases for it, but having "STYPE" instead of "(print)" feels
cleaner.