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.
It's really wrong, because we _should_ be storing PC + 2 in the stack.
And software's definitely gonna bork when we try emulating them, because
they will invariably inspect the stack and assume that's what we have in
there.
But the proper fix is to not actually do next_byte(), and to never
advance PC outside of the execute function. But that's a bigger change
than I want to do at this specific moment.
So, in the meantime, you have me prattling on in a commit message. Lucky
you!
As the Apple II (or rather the 6502 chip) is little-endian, meaning the
least significant byte is the first byte you read going forward, rather
than the last byte.
