It does something, but doesn't work as it should. It could be a few
things including the on/off signal being too slow due to how time
works in the sample generation, but I wanted to at least commit what
I have. It seems to work roughly right according to the forum post
that describes the chip's operation in detail, but there could still
be some glaring bugs
The hope was that this would reduce the amount of copying and bit
shifting required by the frontend to get the data on screen, but
it doesn't seem to offer much advantage, surprisingly. I'll leave
it in though. There are a few other minor tweaks included here to
try to improve the performance a bit
Mortal Kombat 2 was working but somewhere while getting the harte
tests to work, I fixed interrupts to change the flags before they're
pushed to the stack, in order to match the expected behaviour from
the tests when an address error occurs (sr is changed and the stack
push causes the error). I correctly saved the state of sr in the
function for group0 interrupts, to push to the stack later, but the
normal interrupts was saving sr *after* the flags were changed...
Now it saves sr beforehand
I also included some changes to the gfx interface to allow taking
frames, to fix a compile error introduced by the last commit.
I wanted to make this a bit more modular, so it's easier in theory to
write external crates that can reuse bits, and selectively compile in
bits, such as adding new systems or new cpu implementations
There are still some failures on the SBCD, but the logic is identical
to other emulator's calculations, but the test case doesn't seem to be
the way it should behave, so I'll leave it for now
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
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
It's better than it was but there are still minor drop outs due to
a buffer underrun I think (could be other timing issues related to
the update loop or something else). Right now, the audio chips
just have some code to produce sine waves for testing.
There is also a breakpoint error, so that if a read-only memory
location is written to, it will escape to the debugger rather than
exiting the program.
Previously the m68k wasn't masking interrupts with an equal priorty.
I also modified how they work, such that the cpus will check the
controller rather than wait for the notification call
