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