AVR chips often run at less than z80's system clock. This means that
our SPI relay needs to have its own clock to properly communicate
with it. This means that the delay between OUT and IN can't be
hardcoded to 2 NOPs anymore. It needs to be configurable.
Although the SPI Relay driver is RC2014-specific, the SD Card driver
is generic enough to be a subsystem. That's the second subsystem we
add and this warrants, I think, the formalization of a new concept:
protocols.
Among random "better safe than sorry" changes, the real fix is in
changing "4" for "5" above _find declaration. This off-by-one error
had that word, which is the root word in z80, have a 0x01 prev field
instead of a 0x00 one.
When all memory was initialized to zero, it didn't matter, we ended
up hitting 0 prev and considered ourselves properly at the end of
dict.
When memory wasn't initialized, however, we would end up jumping at
all kinds of places, leading to random behavior.
The previous approach of maintaining R> and W> pointers was
conceptually simple, but made INT handler code actually quite
complex.
Now, we maintain indexes instead. It's much easier to perform
bounds checks and to compare for equality, something we have to
do quick in the INT handler.
it seems I left my asm argument harmonization half done here.
Instructions list at B208 doesn't correspond to many actual
mnemonics. This mnemonic here was the worst offender.
I've changed my mind about having documentation in-system. It doesn't
serve much of a purpose and make blkfs significantly heavier.
This commit is the first step in writing a documentation outside of
the blkfs.
Previously, it could never write more than a few bytes before pingpong
getting a mismatch error. Now, I can pingpong Collapse OS binary
without a mismatch.
It's a bit more inconvenient in terms of register protection (BC
is much more generally useful than IY), but it makes tight spots
such as next and execute much faster, so I think it's worth it.
The 1 byte limitation has been effective for a while now, but I
hadn't made the move yet, I wanted to see if the limitation would
cause me problems. It doesn't.
Doing this now slightly facilitates the IY->BC move in z80.
Bootstrapping: if you try to recreate the CVM binary from the
previous commit with this code, you'll have bootstrapping problems.
The first bootstrap will compile a binary with 2-bytes wide cells
but branching conditionals that yields 1-byte cells. That's bad.
I got around the issue by temporarily inserting a "397 399 LOADR"
instruction in cvm/xcomp.fs, right before the xcomp overrides. This
way, I force 1-byte cells everywhere on the first compiliation,
which then allows me to apply the logic change in cvm/vm.c and have
a properly running binary.
There is now no more actual code in stable ABI, only references.
This makes refactoring of this code much easier. For example,
changing IY to BC as the IP register.
