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Update notes in README.

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Cat's Eye Technologies 2014-04-12 12:55:33 +01:00
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@ -102,6 +102,29 @@ two such temporary addresses are never used simultaneously, they may be merged
to the same address. (This is, however, not yet implemented, and may not be
implemented for a while.)
### Pseudo-Instructions ###
Along with instructions which map to the 6502 instruction set, SixtyPical
supplies some instructions which are slightly more abstract and powerful.
For lack of a better term, I'm calling them "pseudo-instructions" here.
(But I would really like a better term.)
In a macro assembler, these pseudo-instructions would be implemented with
macros. However, macros, being textual-substitution-based, are a pain to
analyze. By providing the functions as built-in instructions, we can
easily work them into the type system. Also, there are some macros that are
so common and useful that it makes sense for them to be built-ins, with
standardized, prescriptive names.
Such pseudo-instructions are:
* `copy`, which copies a value from one storage location to another.
This is a typesafe way to copy 16-bit `word`s and `vector`s.
In the future, it may handle 8-bit values and immediate values too.
* `save`, which is not yet implemented. Intended to be used in `with`
blocks when you want to save a value but you don't want to use the
stack. Pairs well with block-level temporary `reserve`d addresses.
### "It's a Partial Solution" ###
SixtyPical does not attempt to force your typed, abstractly interpreted
@ -143,14 +166,56 @@ same time, I'm really not a fan of pointless style — I prefer it when things
are written out explicitly and pedantically. Still, there are places where
an added `foldr` or two would not be unwelcome...
The 6502 semantics, which are arguably RISC-like (load/store architecture)
are translated into an intermediate representation which is arguably CISC-like.
For example, `lda`, `sta`, `ldx`, and `tax` all become kinds of `COPY`
internally. This internal instruction set is much smaller than the 6502's,
and thus is usually easier to analyze.
Notes
-----
This is not quite the right place for this, but I need to write it down
somewhere:
6502 machine code supports an indirect `jmp`, but not an indirect `jsr`.
But an indirect `jsr` is very easy to simulate with an indirect `jmp`.
Instead of
launch:
copy whatever to vector
jsr (vector)
...
Just say
launch:
copy whatever to vector
jsr indirect_jsr
...
indirect_jsr:
jmp (vector)
Then the `rts` at the end of your routine pointed to by `vector` will
return you to where you `jsr`ed.
Because the above is so easy to write, SixtyPical will probably not support
a `jsr (vector)` form (unless it would somehow make analysis easier, but
it probably won't.)
TODO
----
* Initial values for reserved tables
* Character tables ("strings" to everybody else)
* Addressing modes — indexed mode on more instructions
* `jsr (vector)`
* Rename and lift temporaries in nested blocks
* Tail-recursion optimization
* `jmp routine`
* Enforce that `jmp`s come at ends of blocks(?)
* `outputs` on externals
* Routine is a kind of StorageLocation? (Location)?
* remove DELTA -> ADD/SUB (requires carry be notated on ADD and SUB though)
* Test that `pha` restores the A register
* Test poisonining of flags
* Test output of flags