foco65/README.md

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2014-07-19 13:40:30 +00:00
foco65
======
2014-07-19 13:43:00 +00:00
Forth cross-compiler targeting 6502 processors. It needs a 6502
cross-assembler as a backend.
Usage
-----
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
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.
Example
-------
Atari XL/XE example: display character table as 16x16 array.
Uses xasm as a backend.
<pre><code>
[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]
</code></pre>
Atari XL/XE example of defining word in assembly:
wait for keypress and push the pressed key's code
on the parameter stack.
<pre><code>
: 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] ;
</code></pre>
Increase cell at the given address. Shows defining words not
being a valid assembler label.
<pre><code>
create array 16 cells allot
: ++ ( addr -- )
[label] plus_plus
dup @ 1+ swap ! ;
...
array ++
array 1 cell + ++
...
</code></pre>