mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-23 19:58:06 +11:00
forth: move stable ABI stuff at the top of forth.asm
Now we're having a real nice and tidy forth.asm...
This commit is contained in:
Virgil Dupras
parent
f366732424
commit
05045b2aa4
@ -29,7 +29,7 @@ trouble of compiling defs to binary.
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//#define DEBUG
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// in sync with glue.asm
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#define RAMSTART 0x890
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#define RAMSTART 0x850
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#define STDIO_PORT 0x00
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// To know which part of RAM to dump, we listen to port 2, which at the end of
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// its compilation process, spits its HERE addr to port 2 (MSB first)
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Binary file not shown.
325
forth/forth.asm
325
forth/forth.asm
@ -1,34 +1,5 @@
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; Collapse OS' Forth
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;
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; Unlike other assembler parts of Collapse OS, this unit is one huge file.
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;
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; I do this because as Forth takes a bigger place, assembler is bound to take
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; less and less place. I am thus consolidating that assembler code in one
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; place so that I have a better visibility of what to minimize.
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;
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; I also want to reduce the featureset of the assembler so that Collapse OS
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; self-hosts in a more compact manner. File include is a big part of the
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; complexity in zasm. If we can get rid of it, we'll be more compact.
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; Collapse OS Forth's boot binary
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; *** ABI STABILITY ***
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;
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; This unit needs to have some of its entry points stay at a stable offset.
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; These have a comment over them indicating the expected offset. These should
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; not move until the Grand Bootstrapping operation has been completed.
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;
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; When you see random ".fill" here and there, it's to ensure that stability.
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; *** Defines ***
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; GETC: address of a GetC routine
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; PUTC: address of a PutC routine
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;
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; Those GetC/PutC routines are hooked through defines and have this API:
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;
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; GetC: Blocks until a character is read from the device and return that
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; character in A.
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;
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; PutC: Write character specified in A onto the device.
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;
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; *** Const ***
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; Base of the Return Stack
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.equ RS_ADDR 0xf000
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@ -72,39 +43,12 @@
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; (HERE) will begin at a strategic place.
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.equ HERE_INITIAL RAMEND
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; EXECUTION MODEL
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; After having read a line through readline, we want to interpret it. As
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; a general rule, we go like this:
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;
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; 1. read single word from line
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; 2. Can we find the word in dict?
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; 3. If yes, execute that word, goto 1
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; 4. Is it a number?
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; 5. If yes, push that number to PS, goto 1
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; 6. Error: undefined word.
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;
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; EXECUTING A WORD
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;
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; At it's core, executing a word is having the wordref in IY and call
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; EXECUTE. Then, we let the word do its things. Some words are special,
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; but most of them are of the compiledWord type, and that's their execution that
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; we describe here.
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;
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; First of all, at all time during execution, the Interpreter Pointer (IP)
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; points to the wordref we're executing next.
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;
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; When we execute a compiledWord, the first thing we do is push IP to the Return
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; Stack (RS). Therefore, RS' top of stack will contain a wordref to execute
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; next, after we EXIT.
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;
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; At the end of every compiledWord is an EXIT. This pops RS, sets IP to it, and
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; continues.
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; *** Stable ABI ***
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; Those jumps below are supposed to stay at these offsets, always. If they
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; change bootstrap binaries have to be adjusted because they rely on them.
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; Those entries are referenced directly by their offset in Forth code with a
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; comment indicating what that number refers to.
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;
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; We're at 0 here
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jp forthMain
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; 3
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@ -138,7 +82,86 @@
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jp parseDecimal
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jp doesWord
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; *** Code ***
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; *** Boot dict ***
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; There are only 5 words in the boot dict, but these words' offset need to be
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; stable, so they're part of the "stable ABI"
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; Pop previous IP from Return stack and execute it.
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; ( R:I -- )
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.db "EXIT"
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.dw 0
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.db 4
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EXIT:
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.dw nativeWord
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call popRSIP
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jp next
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.db "(br)"
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.dw $-EXIT
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.db 4
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BR:
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.dw nativeWord
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ld hl, (IP)
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ld e, (hl)
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inc hl
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ld d, (hl)
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dec hl
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add hl, de
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ld (IP), hl
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jp next
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.db "(?br)"
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.dw $-BR
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.db 5
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CBR:
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.dw nativeWord
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pop hl
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call chkPS
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ld a, h
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or l
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jr z, BR+2 ; False, branch
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; True, skip next 2 bytes and don't branch
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ld hl, (IP)
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inc hl
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inc hl
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ld (IP), hl
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jp next
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.db ","
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.dw $-CBR
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.db 1
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WR:
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.dw nativeWord
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pop de
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call chkPS
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ld hl, (HERE)
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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ld (HERE), hl
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jp next
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; ( addr -- )
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.db "EXECUTE"
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.dw $-WR
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.db 7
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EXECUTE:
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.dw nativeWord
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pop iy ; is a wordref
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call chkPS
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ld l, (iy)
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ld h, (iy+1)
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; HL points to code pointer
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inc iy
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inc iy
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; IY points to PFA
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jp (hl) ; go!
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; Offset: 00b8
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.out $
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; *** End of stable ABI ***
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forthMain:
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; STACK OVERFLOW PROTECTION:
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; To avoid having to check for stack underflow after each pop operation
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@ -167,11 +190,6 @@ forthMain:
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.bootName:
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.db "BOOT", 0
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.fill 95
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; STABLE ABI
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; Offset: 00cd
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.out $
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; copy (HL) into DE, then exchange the two, utilising the optimised HL instructions.
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; ld must be done little endian, so least significant byte first.
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intoHL:
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@ -183,32 +201,6 @@ intoHL:
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pop de
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ret
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; add the value of A into HL
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; affects carry flag according to the 16-bit addition, Z, S and P untouched.
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addHL:
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push de
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ld d, 0
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ld e, a
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add hl, de
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pop de
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ret
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; Copy string from (HL) in (DE), that is, copy bytes until a null char is
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; encountered. The null char is also copied.
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; HL and DE point to the char right after the null char.
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; B indicates the length of the copied string, including null-termination.
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strcpy:
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ld b, 0
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.loop:
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ld a, (hl)
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ld (de), a
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inc hl
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inc de
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inc b
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or a
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jr nz, .loop
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ret
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; Compares strings pointed to by HL and DE until one of them hits its null char.
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; If equal, Z is set. If not equal, Z is reset. C is set if HL > DE
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strcmp:
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@ -327,7 +319,6 @@ parseDecimal:
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xor a ; set Z
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ret
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; *** Support routines ***
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; Find the entry corresponding to word where (HL) points to and sets DE to
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; point to that entry.
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; Z if found, NZ if not.
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@ -420,26 +411,6 @@ flagsToBC:
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dec bc
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ret
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; Write DE in (HL), advancing HL by 2.
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DEinHL:
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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ret
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; *** Stack management ***
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; The Parameter stack (PS) is maintained by SP and the Return stack (RS) is
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; maintained by IX. This allows us to generally use push and pop freely because
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; PS is the most frequently used. However, this causes a problem with routine
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; calls: because in Forth, the stack isn't balanced within each call, our return
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; offset, when placed by a CALL, messes everything up. This is one of the
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; reasons why we need stack management routines below. IX always points to RS'
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; Top Of Stack (TOS)
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;
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; This return stack contain "Interpreter pointers", that is a pointer to the
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; address of a word, as seen in a compiled list of words.
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; Push value HL to RS
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pushRS:
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inc ix
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@ -485,30 +456,13 @@ chkPS:
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ret nc ; (INITIAL_SP) >= SP? good
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jp abortUnderflow
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; *** Dictionary ***
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; It's important that this part is at the end of the resulting binary.
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; A dictionary entry has this structure:
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; - Xb name. Arbitrary long number of character (but can't be bigger than
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; input buffer, of course). not null-terminated
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; - 2b prev offset
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; - 1b size + IMMEDIATE flag
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; - 2b code pointer
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; - Parameter field (PF)
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;
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; The prev offset is the number of bytes between the prev field and the
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; previous word's code pointer.
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;
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; The size + flag indicate the size of the name field, with the 7th bit
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; being the IMMEDIATE flag.
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;
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; The code pointer point to "word routines". These routines expect to be called
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; with IY pointing to the PF. They themselves are expected to end by jumping
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; to the address at (IP). They will usually do so with "jp next".
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;
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; That's for "regular" words (words that are part of the dict chain). There are
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; also "special words", for example NUMBER, LIT, FBR, that have a slightly
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; different structure. They're also a pointer to an executable, but as for the
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; other fields, the only one they have is the "flags" field.
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abortUnderflow:
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ld hl, .name
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call find
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push de
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jp EXECUTE+2
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.name:
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.db "(uflw)", 0
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; This routine is jumped to at the end of every word. In it, we jump to current
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; IP, but we also take care of increasing it my 2 before jumping
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@ -529,6 +483,8 @@ next:
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jp EXECUTE+2
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; *** Word routines ***
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; Execute a word containing native code at its PF address (PFA)
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nativeWord:
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jp (iy)
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@ -599,99 +555,16 @@ litWord:
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ld (IP), hl
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jp next
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; Pop previous IP from Return stack and execute it.
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; ( R:I -- )
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.db "EXIT"
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.dw 0
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.db 4
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EXIT:
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.dw nativeWord
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call popRSIP
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jp next
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.fill 30
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abortUnderflow:
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ld hl, .name
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call find
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push de
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jp EXECUTE+2
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.name:
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.db "(uflw)", 0
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.db "(br)"
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.dw $-EXIT
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.db 4
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BR:
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.dw nativeWord
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ld hl, (IP)
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ld e, (hl)
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inc hl
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ld d, (hl)
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dec hl
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add hl, de
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ld (IP), hl
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jp next
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.fill 72
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.db "(?br)"
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.dw $-BR
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.db 5
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CBR:
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.dw nativeWord
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pop hl
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call chkPS
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ld a, h
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or l
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jp z, BR+2 ; False, branch
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; True, skip next 2 bytes and don't branch
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ld hl, (IP)
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inc hl
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inc hl
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ld (IP), hl
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jp next
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.fill 15
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.db ","
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.dw $-CBR
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.db 1
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WR:
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.dw nativeWord
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pop de
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call chkPS
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ld hl, (HERE)
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call DEinHL
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ld (HERE), hl
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jp next
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.fill 100
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; ( addr -- )
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.db "EXECUTE"
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.dw $-WR
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.db 7
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; STABLE ABI
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; Offset: 0388
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.out $
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EXECUTE:
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.dw nativeWord
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pop iy ; is a wordref
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call chkPS
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ld l, (iy)
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ld h, (iy+1)
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; HL points to code pointer
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inc iy
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inc iy
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; IY points to PFA
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jp (hl) ; go!
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.fill 677
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; *** Dict hook ***
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; This dummy dictionary entry serves two purposes:
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; 1. Allow binary grafting. Because each binary dict always end with a dummy
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; entry, we always have a predictable prev offset for the grafter's first
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; entry.
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; 2. Tell icore's "_c" routine where the boot binary ends. See comment there.
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.db "_bend"
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.dw $-EXECUTE
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.db 5
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; Offset: 0647
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; Offset: 0253
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.out $
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68
forth/notes.txt
Normal file
68
forth/notes.txt
Normal file
@ -0,0 +1,68 @@
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Collapse OS' Forth implementation notes
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*** EXECUTION MODEL
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After having read a line through readln, we want to interpret it. As a general
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rule, we go like this:
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1. read single word from line
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2. Can we find the word in dict?
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3. If yes, execute that word, goto 1
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4. Is it a number?
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5. If yes, push that number to PS, goto 1
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6. Error: undefined word.
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*** EXECUTING A WORD
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At it's core, executing a word is pushing the wordref on PS and calling EXECUTE.
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Then, we let the word do its things. Some words are special, but most of them
|
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are of the compiledWord type, and that's their execution that we describe here.
|
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|
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First of all, at all time during execution, the Interpreter Pointer (IP) points
|
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to the wordref we're executing next.
|
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|
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When we execute a compiledWord, the first thing we do is push IP to the Return
|
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Stack (RS). Therefore, RS' top of stack will contain a wordref to execute next,
|
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after we EXIT.
|
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|
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At the end of every compiledWord is an EXIT. This pops RS, sets IP to it, and
|
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continues.
|
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|
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*** Stack management
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||||
|
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The Parameter stack (PS) is maintained by SP and the Return stack (RS) is
|
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maintained by IX. This allows us to generally use push and pop freely because PS
|
||||
is the most frequently used. However, this causes a problem with routine calls:
|
||||
because in Forth, the stack isn't balanced within each call, our return offset,
|
||||
when placed by a CALL, messes everything up. This is one of the reasons why we
|
||||
need stack management routines below. IX always points to RS' Top Of Stack (TOS)
|
||||
|
||||
This return stack contain "Interpreter pointers", that is a pointer to the
|
||||
address of a word, as seen in a compiled list of words.
|
||||
|
||||
*** Dictionary
|
||||
|
||||
A dictionary entry has this structure:
|
||||
|
||||
- Xb name. Arbitrary long number of character (but can't be bigger than
|
||||
input buffer, of course). not null-terminated
|
||||
- 2b prev offset
|
||||
- 1b size + IMMEDIATE flag
|
||||
- 2b code pointer
|
||||
- Parameter field (PF)
|
||||
|
||||
The prev offset is the number of bytes between the prev field and the previous
|
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word's code pointer.
|
||||
|
||||
The size + flag indicate the size of the name field, with the 7th bit being the
|
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IMMEDIATE flag.
|
||||
|
||||
The code pointer point to "word routines". These routines expect to be called
|
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with IY pointing to the PF. They themselves are expected to end by jumping to
|
||||
the address at (IP). They will usually do so with "jp next".
|
||||
|
||||
That's for "regular" words (words that are part of the dict chain). There are
|
||||
also "special words", for example NUMBER, LIT, FBR, that have a slightly
|
||||
different structure. They're also a pointer to an executable, but as for the
|
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other fields, the only one they have is the "flags" field.
|
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|
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@ -39,6 +39,7 @@
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: OP1 CREATE C, DOES> C@ A, ;
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0xeb OP1 EXDEHL,
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0x76 OP1 HALT,
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0xe9 OP1 JP(HL),
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0x12 OP1 LD(DE)A,
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0x1a OP1 LDA(DE),
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0xc9 OP1 RET,
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