1. The stack should descend, not ascend;
2. The stack should be pushed byte for byte; meaning, when pushing P or
A, those should consume one byte, not two;
3. The MSB should be pushed first when doing JSR and BRK, which makes
some sense if you were reading the stack from $0100 - $01FF.
Regarding soft switches, we had several we should have been listening
for on both reads and writes, but were only doing so on writes; this is
now fixed.
Regarding statuses, we were incorrectly calculating both carry and
overflow. This should now be fixed, although some quick examinations of
disassembly output suggest there is something else amiss. Debugging will
continue shortly.
This also adds tests for those functions. We have, furthermore, removed
some redundant (and non-externed!) functions from apple2.mem.c which was
the old bank switching code that got moved to apple2.bank.c.
There is one failing test, which I expect to fail at this point; that's
because we need to write a read/write map function for the stack and
zero page so that they use aux memory when BANK_ALTZP is on, and main
memory when not.
To allow this to work, we had to allow the CPU struct to record what the
last opcode/operand/address were, although in truth we only needed the
last address.
Both main and auxiliary memory need to keep an extra 4k of memory that
is bank-switchable, so we have changed to store that memory literally
within the main and aux segments.
The execute function should just work from the PC register. It might
seem to be easier to test by passing an arbitrary opcode into the
function, but because so much of the chip's execution is
context-sensitive (that is, it expects PC to be pointing at the opcode,
to have its operand in front of it, etc.), passing an arbitrary opcode
is not really reflective of what needs to be in place for the function
to work correctly.
