13 KiB
SixtyPical
SixtyPical is a very low-level programming language, similar to 6502 assembly, with block structure and static analysis through abstract interpretation.
It is a work in progress, currently at the proof-of-concept stage.
It is expected that a common use case for SixtyPical would be retroprogramming for the Commodore 64 and other 6502-based computers such as the VIC-20.
Many SixtyPical instructions map precisely to 6502 opcodes. However, SixtyPical is not an assembly language. The programmer does not have total control over the layout of code and data in memory. The language has a type system which distinguishes addresses from non-addresses (16-bit values for which it does not make sense to treat them as addresses.) Some 6502 opcodes have no SixtyPical equivalent. Some SixtyPical instructions are named after 6502 opcodes, but generate slightly different (safer, but intuitively related) sequences of opcodes. Et cetera.
sixtypical
is the reference implementation of SixtyPical. It is written in
Haskell. It can currently parse and analyze a SixtyPical program, and will
eventually be able to compile it to an Ophis assembler listing.
Concepts
Routines
Instead of the assembly-language subroutine, SixtyPical provides the routine as the abstraction for a reusable sequence of code.
A routine may be called, or may be included inline, by another routine.
There is one top-level routine called main
which represents the entire
program.
The instructions of a routine are analyzed using abstract interpretation. One thing we specifically do is determine which registers and memory locations are not affected by the routine.
If a register is not affected by a routine, then a caller of that routine may assume that the value in that register is retained.
Of course, a routine may intentionally affect a register or memory location, as an output. It must declare this. We're not there yet.
Addresses
The body of a routine may not refer to an address literally. It must use a symbol that was declared previously.
An address may be declared with reserve
, which is like .data
or .bss
in an assembler. This is an address into the program's data. It is global
to all routines.
An address may be declared with locate
, which is like .alias
in an
assembler, with the understanding that the value will be treated "like an
address." This is generally an address into the operating system or hardware
(e.g. kernal routine, I/O port, etc.)
Not there yet:
Inside a routine, an address may be declared with
temporary
. This is likestatic
in C, except the value at that address is not guaranteed to be retained between invokations of the routine. Such addresses may only be used within the routine where they are declared. If analysis indicates that two temporary addresses are never used simultaneously, they may be merged to the same address.
An address knows what kind of data is stored at the address:
-
byte
: an 8-bit byte. not part of a word. not to be used as an address. (could be an index though.) -
word
: a 16-bit word. not to be used as an address. -
vector
: a 16-bit address of a routine. Only a handful of operations are supported on vectors:- copying the contents of one vector to another
- copying the address of a routine into a vector
- jumping indirectly to a vector (i.e. to the code at the address contained in the vector (and this can only happen at the end of a routine)
jsr
'ing indirectly to a vector (which is done with a fun generated trick
-
byte table
: (not yet implemented) a series ofbyte
s contiguous in memory starting from the address. this is the only kind of address that can be used in indexed addressing.
Blocks
Each routine is a block. It may be composed of inner blocks, if those inner blocks are attached to certain instructions.
SixtyPical does not have instructions that map literally to the 6502 branch
instructions. Instead, it has an if
construct, with two blocks (for the
"then" and else
parts), and the branch instructions map to conditions for
this construct.
Similarly, there is a repeat
construct. The same branch instructions can
be used in the condition to this construct. In this case, they branch back
to the top of the repeat
loop.
The abstract states of the machine at each of the different block exits are merged during analysis. If any register or memory location is treated inconsistently (e.g. updated in one branch of the test, but not the other,) that register cannot subsequently be used without a declaration to the effect that we know what's going on. (This is all a bit fuzzy right now.)
There is also no rts
instruction. It is included at the end of a routine,
but only when the routine is used as a subroutine. Also, if the routine
ends by jsr
ing another routine, it reserves the right to do a tail-call
or even a fallthrough.
There are also with instructions, which are associated with an opcode
that has a natural symmetrical opcode (e.g. pha
, sei
). These instructions
take a block. The natural symmetrical opcode is inserted at the end of the
block.
Unsupported Opcodes
6502 opcodes with no language-level equivalent instructions in SixtyPical
are brk
, cli
, pla
, plp
, rti
, and rts
. These may be
inserted into the output program as a SixtyPical → 6502 compiler sees fit,
however.
Note to self, the pl
opcodes do change flags.
Instruction Support so far
A X
indicates unsupported. A !
indicates will-not-support.
Funny syntax indicates use of a special form.
In these, absolute
must be a reserve
d or locate
d address.
X adc #immediate
X adc absolute
X and #immediate
X and absolute
X asl
X asl absolute
if bcc { block } else { block }
if bcs { block } else { block }
if beq { block } else { block }
X bit absolute
if bmi { block } else { block }
if bne { block } else { block }
if bpl { block } else { block }
if bvc { block } else { block }
if bvs { block } else { block }
clc
cld
clv
cmp #immediate
cmp absolute
cpx #immediate
cpx absolute
cpy #immediate
cpy absolute
dec absolute
dex
dey
X eor #immediate
X eor absolute
inc absolute
inx
iny
* jsr routine
X jsr vector
X jmp routine
* jmp vector
lda #immediate
lda absolute
ldx #immediate
ldx absolute
ldy #immediate
ldy absolute
X lsr
X lsr absolute
nop
X ora #immediate
X ora absolute
X pha { block }
X php { block }
X rol
X rol absolute
X ror
X ror absolute
X sbc #immediate
X sbc absolute
sec
sed
X sei { block }
sta absolute
stx absolute
sty absolute
tax
tay
X tsx
txa
X txs
tya
TODO
- Parse HEX values like $40A3
- Tables
- Character tables ("strings" to everybody else)
- External routines
- Work out the analyses again and document them
repeat jmp
- Addressing modes; rename instructions to match
- no two routines with same name
Tests
-> Tests for functionality "Parse SixtyPical program"
-> Functionality "Parse SixtyPical program" is implemented by
-> shell command "bin/sixtypical parse %(test-file)"
-> Tests for functionality "Check SixtyPical program"
-> Functionality "Check SixtyPical program" is implemented by
-> shell command "bin/sixtypical check %(test-file)"
main
must be present.
| routine main {
| nop
| }
= True
| routine frog {
| nop
| }
? missing 'main' routine
A program may reserve and assign.
| reserve word score
| assign word screen 1024
| routine main {
| lda screen
| tax
| tay
| cmp score
| ldx score
| txa
| ldy score
| tya
| }
= True
All declarations (reserve
s and assign
s) must come before any routines
.
| routine main {
| lda score
| }
| reserve word score
? expecting "routine"
All locations used in all routines must be declared first.
| reserve word score
| routine main {
| lda score
| cmp screen
| }
? undeclared location
Even in inner blocks.
| reserve word score
| assign word screen 1024
| routine main {
| lda score
| cmp screen
| if beq {
| lda score
| } else {
| lda fnord
| }
| }
? undeclared location
No duplicate declarations.
| reserve word score
| assign word score 4000
| routine main {
| nop
| }
? duplicate declaration
We can jump to a vector.
| reserve vector blah
| routine main {
| jmp blah
| }
= True
We can't jump to a word.
*| reserve word blah
*| routine main {
*| jmp blah
*| }
*? wtf
-> Tests for functionality "Emit ASM for SixtyPical program"
-> Functionality "Emit ASM for SixtyPical program" is implemented by
-> shell command "bin/sixtypical emit %(test-file)"
| reserve word score
| assign word screen 1024
| routine main {
| lda #4
| ldx #0
| ldy #255
| lda screen
| inc screen
| tax
| inx
| dex
| stx score
| tay
| iny
| dey
| sty score
| cmp score
| cmp #30
| ldx score
| cpx screen
| cpx #31
| txa
| ldy score
| cpy screen
| cpy #32
| tya
| sta screen
| dec screen
| clc
| cld
| clv
| sec
| sed
| }
= .org 0
= .word $0801
= .org $0801
= .byte $10, $08, $c9, $07, $9e, $32, $30, $36, $31, $00, $00, $00
= jmp main
= score: .word 0
= .alias screen 1024
= main:
= lda #4
= ldx #0
= ldy #255
= lda screen
= inc screen
= tax
= inx
= dex
= stx score
= tay
= iny
= dey
= sty score
= cmp score
= cmp #30
= ldx score
= cpx screen
= cpx #31
= txa
= ldy score
= cpy screen
= cpy #32
= tya
= sta screen
= dec screen
= clc
= cld
= clv
= sec
= sed
= rts
| assign word screen 1024
| routine main {
| lda screen
| cmp screen
| if beq {
| tax
| } else {
| tay
| }
| sta screen
| }
= .org 0
= .word $0801
= .org $0801
= .byte $10, $08, $c9, $07, $9e, $32, $30, $36, $31, $00, $00, $00
= jmp main
= .alias screen 1024
= main:
= lda screen
= cmp screen
= BEQ _label_1
= tay
= jmp _past_1
= _label_1:
= tax
= _past_1:
= sta screen
= rts
| assign byte screen 1024
| reserve byte zero
| routine main {
| ldy zero
| repeat bne {
| inc screen
| dey
| cpy zero
| }
| sty screen
| }
= .org 0
= .word $0801
= .org $0801
= .byte $10, $08, $c9, $07, $9e, $32, $30, $36, $31, $00, $00, $00
= jmp main
= .alias screen 1024
= zero: .byte 0
= main:
= ldy zero
=
= _repeat_1:
= inc screen
= dey
= cpy zero
= BNE _repeat_1
= sty screen
= rts
Nested ifs.
| routine main {
| if beq {
| if bcc {
| lda #0
| } else {
| if bvs {
| lda #1
| } else {
| lda #2
| }
| }
| } else {
| lda #3
| }
| }
= .org 0
= .word $0801
= .org $0801
= .byte $10, $08, $c9, $07, $9e, $32, $30, $36, $31, $00, $00, $00
= jmp main
= main:
= BEQ _label_3
= lda #3
= jmp _past_3
= _label_3:
= BCC _label_2
= BVS _label_1
= lda #2
= jmp _past_1
= _label_1:
= lda #1
= _past_1:
= jmp _past_2
= _label_2:
= lda #0
= _past_2:
= _past_3:
= rts
Installing an interrupt handler (at the Kernal level, i.e. with CINV)
| assign byte screen 1024
| assign vector cinv 788
| reserve vector save_cinv
|
| routine main {
| sei {
| copy vector cinv to save_cinv
| copy routine our_cinv to cinv
| }
| }
|
| routine our_cinv {
| inc screen
| jmp save_cinv
| }
= .org 0
= .word $0801
= .org $0801
= .byte $10, $08, $c9, $07, $9e, $32, $30, $36, $31, $00, $00, $00
= jmp main
= .alias screen 1024
= .alias cinv 788
= save_cinv: .word 0
= main:
= sei
= lda cinv
= sta save_cinv
= lda cinv+1
= sta save_cinv+1
= lda #<our_cinv
= sta cinv
= lda #>our_cinv
= sta cinv+1
= cli
= rts
=
= our_cinv:
= inc screen
= jmp (save_cinv)
= rts