foco65 ====== Forth cross-compiler targeting 6502 processors. It needs a 6502 cross-assembler (e.g. [xasm](https://github.com/pfusik/xasm)) as a backend. Usage ----- ```sh foco65 [OPTIONS] INPUT-FILE ``` OPTIONS: -h display help -p ADDR,--pstack-bottom=ADDR parameter stack bottom address -s SECTS,--sections=SECTS specify comma separated list of sections default: init,boot,data,code -S INT,--pstack-SIZE=INT parameter stack size Example: ```sh $ foco65 foo.forth > foo.asx ``` Words ----- `:` `@` `0=` `1-` `1+` `2/` `2*` `2@` `2!` `and` `c!` `c@` `cmove` `count` `d-` `d+` `d=` `do` `drop` `dup` `i` `j` `loop` `+loop` `lshift` `<=` `<` `>=` `>` `-` `+` `or` `over` `rshift` `rsp` `sp` `swap` `unloop` `u<` `u>` `while` `<>` `=` `!` `[` `]` `[code]` `[end-code]` `cell` `cells` `not` `[section]` `variable` `2variable` `constant` `create` `,` `c,` `,'` `'` `,"` `"` `allot` `lit` `\` `(` `recursive` `[label]` `*` `/` Internals --------- Type: indirect-threaded. Cell size is 16 bits. Parameter stack pointer is kept in register `X`. Parameter stack pointer is decremented before write (stack push) and incremented after read (stack pop). Hardware stack (page $01) is used as return stack. Instruction pointer and other work registers are kept in page zero occupying total of 12 bytes. After initializing interpreter internal state user-defined word `main` is executed. Generated code is placed into sections which are output in the order: `init`, `boot`, `data`, `code` or other - specified by the user. Examples -------- Atari XL/XE executable skeleton. Uses xasm a a backend.
[section] init
[code]
org $2000
[end-code]
[section] code
: main
begin
...
again ;
[code]
run boot
[end-code]
Atari XL/XE example: display character table as 16x16 array.
Uses xasm as a backend.
[section] init
[code]
org $3000
[end-code]
[section] code
$230 constant dladr
variable screen
variable cursor
variable line
: cursor-next ( -- u )
cursor @ dup 1+ cursor ! ;
: put-char ( c -- )
cursor-next c! ;
: set-cursor ( u -- )
screen @ + cursor ! ;
: main
dladr @ 4 + @ screen !
0 line !
16 0 do
line @ set-cursor
line @ 40 + line !
16 0 do
i j 4 lshift or put-char
loop
loop
begin again ;
[code]
run boot
[end-code]
Atari XL/XE example of defining word in assembly:
wait for keypress and push the pressed key's code
on the parameter stack.
: get-char ( -- c )
[code]
lda #0
dex
sta pstack,x
stx w
jsr do_gc
ldx w
dex
sta pstack,x
jmp next
do_gc
lda $E425
pha
lda $E424
pha
rts
[end-code] ;
Increase cell at the given address. Shows defining words not
being a valid assembler label.
create array 16 cells allot
: ++ ( addr -- )
[label] plus_plus
dup @ 1+ swap ! ;
...
array ++
array 1 cell + ++
...