Previously it was going line by line, but that makes it hard to
properly parse multiline comments, so I modified it to include line
terminators in the token stream. I also added parsing of /* */
and | \n comment types. There is still a problem with line numbers
in the post-parsing phases, but they seem correct in the parser/lexer
stage. It's still not able to parse the syscall.s file from Computie
but it's mostly just issues with named constants preceeded by a
"#" or "-" character. As for the encoding stage, it has a problem
with a move instruction that uses a label.
It can encode some basic instructions but not the more complicated
addressing modes or special instructions. It can keep track of
labels and patch the displacement addresses after assembling the
output data, but it doesn't check for duplicates or that a label
has been declared before it appears. It also doesn't take into
account the origin yet. To run it, there is an m68kas command
that will take a file and print the data:
```
cargo run -p moa --bin m68kas <filename>
```
It's not yet tied into the rest of the system, but could be used in
the debugger to allow insertion of new code into a running system.
In order to more accurately emulate the VDP, the main draw loop is
now going through each pixel on the screen and calculates the various
cells that should be displayed, gets the exact pixel data, and then
draws lines them all up in priority-order, and whichever is the first
non-mask pixel colour gets put into the frame buffer. It's rather
verbose and duplicative, but I'll fix it up now that I have something
working
It's a bit weirdly implemented because the Addressable trait doesn't
have access to System, so it has to set a flag on the Bus which is
then checked during the step function in System to activate the
breakpoint if a watched memory location was written to
It turned out to be an issue with the interrupts and when the
vertical interrupt was triggered vs when the vertical blanking
bit was set. The interrupt code in sonic 2 tries to read the
status bit after the vint occurs, and if the vblank bit is set,
it runs the Vint_Level function, but the hacky code I wrote
turned the vblanking bit on after 14ms and off when it triggered
the vint, instead of turning it on at 15ms, and off at 1.2ms, with
the int occuring at the *start* of the time the blanking bit is
set. So the code had been waiting for 14ms after the vint until
it actually started processing thing, which didn't complete before
the next vint, so it only ran the main game loop every 33.2ms which
is why doubling the speed of the simulated execution time made it
seem about the right speed
The hscroll table was multiplying by 2 (because scroll a and b values
are next to each other) but it should have multiplied by 4 because
each value is also 2 bytes and the array is of u8.
I added hscroll by-line support by using a different function for the
line scroll vs the cell or whole screen scrolling. There are still
a bunch of glitches in scroll b's scroll values that I need to fix
The TH counter in the genesis controller code was increasing each
time the TH bit changed state instead of only in one direction.
Surprisingly it worked before, and fixing it made it not work in
Sonic 2, but after adding the 1.5ms timer to reset the TH counter,
it worked again. I guess Sonic2 only reads the 3 buttons instead
of all 6. It should now work with both 3 and 6 button games
