Doing SPI bit-banging through a controller port is already really
slow, but doing so with the Forth version of (spix) was really,
really slow.

With this pure z80 version of (spix), it's more bearable.

At-XY+EMIT is slow compared to direct CELL! usage. It is seen very
clearly on a SMS when VE is doing its initial clrscr (yes, I could
manage to load VE from a SD card and run it on a real SMS!).

The grid protocol wasn't there when I wrote VE initially. I only had
AT-XY. Now that we have a solid protocol to build on, let's do it.

I hadn't noticed yet, but making CVM use the Grid subsystem made
me lose scrolling. It's fine because that scrolling was "artificial"
in the sense that it was provided by curses, not Collapse OS and I
prefer having something that closer emulates a real machine.

However, CVM didn't properly clear the new line when entering it.
Fixed.

Scrolling behavior will come back when it's implemented in the Grid
subsystem.

In CURSOR!, I was using a write commande to read from VRAM and the
emulator didn't properly behave and did as if everything was fine.

The result on a real SMS was that the cursor would contain the
inverted glyph of the contents of the *old* cursor position.

I do this by adding an inverted version of all glyphs in the upper
range of the pattern memory. This is a big waste of the pattern
space (only one inverted character is needed at once), but it's the
simplest way to proceed. I'll change this if I ever need more
pattern space.

Also, remove _blank. It was wastefully blanking the whole memory.
Only the name table needs to be blanked on initialization.

This required the change of CURSOR! signature: we now supply it
with both old and new cursor positions.

Also, fix broken _bs in Grid subsystem.

Replace the "g" arg (glyph) with "c" (character). The reason why "g"
was used was to save a "0x20 -" operation at all CELL! implementations,
but this came with too big a drawback: it made CELL! hardly usable
outside of the Grid subsystem, mostly because the user of CELL! would
often have to do "0x20 -".

For example, I want the SMS's Pad driver to use CELL! directly instead
of having to do EMIT+XYPOS-messing-around. I would have had to do a
"0x20 -" there.

With the move of CVM's forth to the grid protocol, we've lost the
cursor's visual indication. Now, we have it back.

The challenge now is in implementing it in SMS' text mode. In mode
4, it's easy to mark a cell as inverted, but in text mode, that's
not possible.

In VE on the SMS, the first contents line would always be cleared
because of NEWLN being called when the FBUF would spit its last
char. Inconvenient...

I've added a "graphical" mode to the grid subsystem to inhibit this
behavior in a graphical situation such as in VE.

Also, write a more complete Grid documentation.

Also, fixed broken AT-XY in Grid...

Working in "blk/" folder from a modern system is harder than it
should be. Moving blocks around is a bit awkward, grepping is a
bit less convenient than it could be, git blame has troubles
following, etc.

In this commit, we modify blkpack and blkunpack to work with single
text files with blocks being separated by a special markup.

I think this will make the code significantly more convenient to
work into.

I wanted to make CVM's forth use the Grid subsystem, but doing so
would break the stage binary. Hence, this split.

Previously, display would be completely broken. We have yet to add
a way to display the "right" part of a buffer on such smaller
displays.

I'm planning on de-hardcoding columns in VE a bit to add support
for screens narrower than 67 columns. There's a lot of hardcoding.

Let's begin with not using core's LIST anymore. This allows us to
spit 1-16 numbers only at startup.

Because that mode behaves exactly like in a regular TMS9918, a new
driver for TMS9918 has been added in blkfs and SMS' VDP now uses it.

Also, fix broken 5x7 font.

I'm planning on supporting Text Mode soon, and SMS' VDP, when mode
4 is not active, behaves mostly like a regular TMS9918.

By having this behavior in a separate unit, we'll be able to use it
in other systems.

Also, rename CLRLN to NEWLN and make it clear that it's only called
on entering a new line. This way, we can set Z offset in there for
the TI-84+ LCD driver.

Instead of clearing the rest of the line on a _lf, it's simpler
to just clear any new line we're entering into.

Rename ROWS to LINES (it's what VE uses). Also, don't use COLS and
LINES as immediates in the Grid subsystem: we expect those words to
be available at runtime.

The goal is to offload the SMS VDP driver a little bit.

it has been removed from the core.

On the real machine, I ended up at some point getting a weird "bottom
mirroring" issue. It turns out that it was because when I revamped my
VDP flags in an earlier commit, I hadn't read the whole technical
notes about register $02 and falsely thought that B0 was ignored. No
it's not. When set, it mirrors the bottom 8 rows.

I've noticed that under certain conditions, such as a stack overflow,
I would segfault, something I though was impossible because my memory
size is 0x10000 and all my integer variables are uint16_t.

After having re-read my C handbook, it seems I wasn't sufficiently
knowledgeable about type conversion rules.

It isn't used in there anymore. Moved it to VE, the only place
where it's used.

If a line has a char below 0x20, we consider the line ended, we
stop the EMIT loop for this line and spit our NL.

This makes LIST stop wasting rows in environments with a tight
screen.

This allows us (in the following commit), to stop unvariably
spitting 64 chars by line in LIST. This way, short lines don't use
3 rows per line (the line number uses 3 chars, which brings us to
67 chars per line).

If we don't do that, we end up with the old contents of the line
being kept at the right of the printed line.

I was sampling DO at the wrong moment, so my input was always
one-off.

why did I think that I could read from it?

NetBSD doesn't have ncurses. Linking to curses doesn't seem to change
anything. Tried on OpenBSD and Ubuntu.

The '2' key on my PS/2 keyoard never worked on Collapse OS, I
wasn't sure why. I thought the keyboard was broken, but then I
tried another one, still broken. But it's only the '2'!

The KC sent is 0x1f. Is it a timing problem with the ATtiny? I
have yet to wire my prototype for logic probing. Meanwhile, let's
apply a band-aid.

Previous instructions would only work with an AT28C64. Now, it also
work with an AT28C256.

Add _TRA!, _THA!, _TRB!, _THB! routines to easily handle those pins'
value without stepping on other pins like the drivers previously
did. For SDC driver, it's going to be important soon because it turns
out that I can't get away with "always on" CS, so I'll need a scheme
where it's important that TH/TR pins have stable values.

Recipes contain bits and pieces of hardware-related knowledge, but
these bits feel sparse. I've been wanting to consolidate hardware-
related documentation for a while, but always fell at odds with the
recipes organisation.

We don't have recipes anymore, just a /doc/hw section that contains
hardware-related documentation which often translate to precise
instructions to run Collapse OS on a specific machine.

With this new organisation, I hope to end up with a better, more
solid documentation.

Theoretically, it works. I can access an emulated SD card on it.

Will it work on real hardware?

I've also made SMS emulation faster. It was unbearably slow for SDC
access.

My idea of plugging a RC2014 bridge directly onto a Sega Master System
cartridge doesn't work. The SMS eats all I/O addr space, we can't use
it. Therefore, this naive idea, in the emulator, of reusing sdc.c in
sms.c as-is, doesn't work either.

I'll have to find another way of communicating to a SPI device on the
SMS. I'll probably do it through a controller port. Meanwhile, I need
to decouple SPI from SDC in the emulator code so that I can reuse
sdc.c. This is what is done here.

There are many situations where it can be useful. Worth it.

This allows us to remove AMOVE* words.