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cc0.asm
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cc0.asm
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; ===============================================
; CamelForth for the Intel 8051
; (c) 1994,1997,1999 Bradford J. Rodriguez
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 3 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <http://www.gnu.org/licenses/>.
; Commercial inquiries should be directed to the author at
; 115 First St., #105, Collingwood, Ontario L9Y 4W3 Canada
; or via email to [email protected]
;
; ===============================================
; CAMEL51.ASM: Code Primitives
; Source code is for the A51 assembler.
; Forth words are documented as follows:
;x NAME stack -- stack description
; where x=C for ANS Forth Core words, X for ANS
; Extensions, Z for internal or private words.
;
; Subroutine-Threaded Forth model for Intel 8051
; 16 bit cell, 8 bit char, 8 bit (byte) adrs unit
; split Code & Data spaces
; 8051 PC = Forth IP Interpreter Pointer
; SP = RSP Return Stack Pointer low
; RSP high byte = 0
; R0 = PSP Parameter Stack Ptr low
; PSP high = UP
; reg 08 = P2 = UP User area Pointer high
; (and PSP high), UP low = 0
; DPTR = TOS (top Param. Stack item)
; A,B,R1-R5 = temporaries
; (no W register is defined)
; R6,R7 = loop index
; reg 09-7F = return stack
; ===============================================
; REVISION HISTORY
; $Log: Camel51.asm,v $
; v1.6 18 Aug 99 Fixed FM/MOD (again).
;
; Revision 1.5 1997/05/28 23:03:52 brad
; v1.5 Added multitasker words. 28 Mar 97
; Corrected memory map comments.
; Fixed UM* bug.
; Fixed FM/MOD bug, per Ed Smeda (thanks!)
; Fixed >BODY to return Data adrs, per ANS.
; Moved SWAP from REPEAT to WHILE, per ANS.
; ABORT" ?ABORT now use IS" and ITYPE.
; Fixed WORDS to ignore smudge bit.
; Fixed IWORD to return Code address.
; Renamed ROMDICT,RAMDICT to CODERAM,DATARAM
; v1.4 changed QUIT to type CR even 9 Nov 96
; if STATE<>0, to support downloading.
; Added example I/O.
; v1.3 changed PLUSLOOPSENSE to 17 Mar 96
; PLUSLPSENSE (for some A51 assemblers)
; v1.2 fixed names of KEY? and S>D
; v1.1 bug fixes for split I & D mem 14 Mar 95
; in COLD: changed CMOVE to I->D
; in XISQUOTE: changed COUNT to ICOUNT
; in LIT: uses MOVC instead of MOVX
; in FIND: changed NFA>LFA @ to NFA>LFA I@
; in QUIT: changed TYPE to ITYPE
; v1.0 alpha test version, 12 Dec 94
; ===============================================
; Forth linkage
.equ link,0
.equ IMMED,1 ; flag for Immediate word
; 8051 EQUATES
.equ dr2,0x02 ; r2-r5 accessed as
.equ dr3,0x03 ; direct registers;
.equ dr4,0x04 ; required for PUSH and
.equ dr5,0x05 ; POP instructions.
.equ dr6,0x06 ; Assumes register bank 0
.equ dr7,0x07 ; is selected.
.equ UP,0x08
; FORTH MEMORY MAP EQUATES
; Memory map:
; regs 8-7Fh Return stack, 120 bytes, grows up
; 0000h Forth kernel
; E000h Forth dictionary (program)
; F000h Forth dictionary (user RAM)
; UAREA-100h Task Save Area, 128 bytes
; UAREA-80h Terminal Input Buffer, 128 bytes
; UAREA=FE00h User area, 128 bytes
; UAREA+80h Parameter stack, 128B, grows down
; UAREA+100h HOLD area, 40 bytes, grows down
; UAREA+128h PAD buffer, 88 bytes
; UAREA+180h Leave stack, 128 bytes, grows up
; See also the definitions of U0, S0, and R0
; in the "system variables & constants" area.
; A task w/o terminal input requires 200h bytes.
; Double all except TIB and PAD for 32-bit CPUs.
; Initial RAM & ROM pointers for CamelForth.
.equ coderam,0x0e000 ; where new code goes
.equ dataram,0x0f000 ; where data goes
.equ UPHI,0xFD ; Uarea at FE00 hex
.org 0x0000
; RESET AND INTERRUPT VECTORS ===================
ljmp reset
; ljmp ie0
; ie0: reti
; .skip 4
; ljmp clock ; ljmp tf0
; tf0: reti
; .skip 4
; ljmp ie1
; ie1: reti
; .skip 4
; ljmp tf1
; tf1: reti
; .skip 4
; ljmp riti
; riti: reti
; .skip 4
; ljmp tf2
; tf2: reti
;
reset: mov ie,#0 ; disable all irpts
.equ FWT,0xab
.equ FADDRL,0xac
.equ FADDRH,0xad
.equ FLC,0xae
.equ FWDATA,0xaf
.equ U0CSR,0x86
.equ U0UCR,0xc4
.equ U0GCR,0xc5
.equ U0DBUF,0xc1
.equ U0BAUD,0xc2
.equ IRCON2,0xe8
.equ P0DIR,0xfd
.equ P0SEL,0xf3
.equ CLKCON,0xc6
.equ _IDP ,0x0a
.equ _LATEST ,0x0c
.equ WORDBUF ,0x0e
.equ RSP0, 0x40
.equ S0, 0xff
; 76543210
mov CLKCON,#0b10001000 ; external crystal
mov FWT,#0x2a ; flash write timer
mov P0SEL, #0b00001100 ; UART0
mov U0CSR, #0b11000000 ; 8N1
mov U0UCR, #0b10000010
mov U0GCR, #12 ; 115200
mov U0BAUD,#34
mov UP,#UPHI
mov r0,#S0 ; param stack at FEFF
mov sp,#RSP0
ljmp COLD ; enter Forth interpreter
; SERIAL I/O ====================================
; See TI DN112: Using UART in CC111x
;C EMIT c -- output character to console
.drw link
.set link,*+1
.db 0,4,"EMIT"
EMIT:
clr IRCON2.1
mov U0DBUF,dpl ; output TOS char to UART
w: jnb IRCON2.1,w
clr IRCON2.1
ajmp poptos ; pop new TOS
;C KEY -- c get character from keyboard
.drw link
.set link,*+1
.db 0,3,"KEY"
KEY:
mov a,U0CSR
jnb acc.2,KEY
acall DUP
mov dpl,U0DBUF ; get new char in TOS
mov dph,#0
ret
;X KEY? -- f return true if char waiting
.drw link
.set link,*+1
.db 0,4,"KEY?"
QUERYKEY:
acall DUP
mov a,scon ; get rx flag in carry
rrc a
ajmp cyprop ; propagate that thru TOS
; LOOP FACTORS ==================================
bounds: acall OVER
acall PLUS
ajmp SWOP
break: mov a,@r0
cjne a,dpl,exit1
inc r0
mov a,@r0
dec r0
cjne a,dph,exit1
acall TWODROP
sjmp EXIT
; INTERPRETER LOGIC =============================
; NEXT and ENTER are not needed for Subroutine
; Threading. EXIT may be used in high level code.
;C EXIT -- exit a colon definition
.drw link
.set link,*+1
.db 0,4,"EXIT"
EXIT: dec sp ; discard ret adrs in caller
dec sp
exit1: ret ; return to caller's caller
;Z LIT -- x fetch inline literal to stack
.drw link
.set link,*+1
.db 0,3,"LIT"
LIT: dec r0 ; push old TOS
mov @r0,dph
dec r0
mov @r0,dpl
pop dph ; get return address
pop dpl
clr a
movc a,@a+dptr ; get literal low byte
inc dptr
mov r2,a
clr a
movc a,@a+dptr ; get literal high byte
inc dptr
push dpl ; restore updated ret adr
push dph
mov dph,a ; put literal in TOS
mov dpl,r2
ret
;C EXECUTE i*x xt -- j*x execute Forth word
;C at 'xt'
.drw link
.set link,*+1
.db 0,7,"EXECUTE"
EXECUTE: push dpl ; push addr onto r.stack,
push dph ; then pop new TOS->DPTR
; 'ret' in poptos will then execute
; desired word; its 'ret' will return to
; EXECUTE's caller.
ajmp poptos
XISQUOTE: acall RFROM
acall COUNT
lcall TWODUP
acall PLUS
ajmp EXECUTE
; DEFINING WORDS ================================
;Z CELL -- n size of one cell
.drw link
.set link,*+1
.db 0,4,"CELL"
CELL: acall DOCON
.drw 2
;C VARIABLE -- define a Forth VARIABLE
; CREATE CELL ALLOT ;
; Action of ROMable variable is that of CONSTANT;
; the constant holds the RAM address.
.drw link
.set link,*+1
.db 0,8,"VARIABLE"
VARIABLE: lcall CREATE
acall CELL
ljmp ALLOT
;C CONSTANT -- define a Forth constant
; CREATE CELL NEGATE IALLOT I, Harvard model
; DOES> (machine code fragment)
; Note that the constant is stored in Code space.
.drw link
.set link,*+1
.db 0,8,"CONSTANT"
CONSTANT: lcall CREATE
lcall CELL
lcall NEGATE
lcall IALLOT
lcall ICOMMA
lcall XDOES
; DOCON, code action of CONSTANT,
; entered by CALL DOCON
docon: ; -- x exec action of constant
dovar: ; -- a-addr exec action of ROMable var
docreate: ; -- a-addr exec action of Harv.CREATE
dec r0 ; push old TOS
mov @r0,dph
dec r0
mov @r0,dpl
pop dph ; get addr of param field
pop dpl ; (in Code memory!)
ajmp FETCH ; go fetch its contents
; DOUSER, code action of USER,
; entered by CALL DOUSER
douser: acall pushtos ; push old TOS
pop dph ; get addr of param field
pop dpl ; (in Code memory!)
acall FETCH ; go fetch its contents
add a,UP ; add UP:00 to offset
mov dph,a ; NB. IFETCH leaves A=DPH
ret
; DOCREATE's action is for a table in RAM.
; DOROM is the code action for a table in ROM;
; it returns the address of the parameter field.
; Entered by CALL DOROM
dorom: acall pushtos ; push old TOS
pop dph ; param field adrs -> TOS
pop dpl
ret
; DODOES, code action of DOES> clause
; (internal code fragment, not a Forth word)
; entered by LCALL fragment
; address of data
; ...
; fragment: LCALL DODOES
; high-level thread
; Enters high-level thread with address of
; data on top of stack. HARVARD MODEL: the data
; (in Data space) does NOT follow LCALL fragment
; (in Code space); instead, the address of the
; data is appended after LCALL fragment.
dodoes: ; -- a-addr support routine for DOES>
dec r0 ; push old TOS
mov @r0,dph
dec r0
mov @r0,dpl
pop dr5 ; addr of DOES> clause
pop dr4 ; Forth code
pop dph ; addr of defined word's
pop dpl ; Param. field
push dr4 ; restore Forth code addr
push dr5
ajmp FETCH ; fetch adrs from P.field
; & go do the DOES> code
; STACK OPERATIONS ==============================
;C DUP x -- x x duplicate top of stack
.drw link
.set link,*+1
.db 0,3,"DUP"
DUP:
pushtos: dec r0 ; push hi byte of TOS
mov @r0,dph
dec r0 ; push lo byte of TOS
mov @r0,dpl
ret
;C ?DUP x -- 0 | x x DUP if nonzero
.drw link
.set link,*+1
.db 0,4,"?DUP"
QDUP: mov a,dph
orl a,dpl
jnz pushtos
ret
;C DROP x -- drop top of stack
.drw link
.set link,*+1
.db 0,4,"DROP"
DROP:
poptos: mov dpl,@r0 ; pop lo byte -> TOS
inc r0
mov dph,@r0 ; pop hi byte -> TOS
inc r0
ret
;C SWAP x1 x2 -- x2 x1 swap top two items
.drw link
.set link,*+1
.db 0,4,"SWAP"
SWOP: mov a,@r0
xch a,dpl
mov @r0,a
inc r0
mov a,@r0
xch a,dph
mov @r0,a
dec r0
ret
;C OVER x1 x2 -- x1 x2 x1 per stack diagram
.drw link
.set link,*+1
.db 0,4,"OVER"
OVER:
mov dr3,@r0 ; a:r3 is x1
inc r0
mov a,@r0
dec r0
dec r0 ; push hi byte of TOS
mov @r0,dph
dec r0 ; push lo byte of TOS
mov @r0,dpl
mov dph,a
mov dpl,r3
ret
;C ROT x1 x2 x3 -- x2 x3 x1 per stack diagram
.drw link
.set link,*+1
.db 0,3,"ROT"
ROT: ; x3 is in TOS
mov dr4,@r0 ; pop x2 -> r5:r4
inc r0
mov dr5,@r0
inc r0
mov dr2,@r0 ; pop x1 -> a:r2
inc r0
mov a,@r0
mov @r0,dr5 ; push x2
dec r0
mov @r0,dr4
dec r0
mov @r0,dph ; push x3
dec r0
mov @r0,dpl
mov dph,a ; TOS now x1
mov dpl,r2
ret
;C >R x -- R: -- x push to return stack
.drw link
.set link,*+1
.db 0,2,">R"
TOR: pop dr3 ; save ret addr in r3:r2
pop dr2
push dpl ; push lo byte*
push dph ; push hi byte*
push dr2 ; restore ret addr
push dr3
sjmp poptos ; pop new TOS
;* NB. stored lo:hi in regs because SP increments
;C R> -- x R: x -- pop from return stack
.drw link
.set link,*+1
.db 0,2,"R>"
RFROM: dec r0 ; push old TOS
mov @r0,dph
dec r0
mov @r0,dpl
pop dr3 ; save ret addr in r3:r2
pop dr2
pop dph ; pop hi byte
pop dpl ; pop lo byte
push dr2 ; restore return address
push dr3
ret
;C R@ -- x R: x -- x fetch from rtn stack
.drw link
.set link,*+1
.db 0,2,"R@"
RFETCH: dec r0 ; push old TOS
mov @r0,dph
dec r0
mov @r0,dpl
mov r1,sp ; get copy of SP
dec r1 ; skip return address
dec r1
mov dph,@r1 ; fetch 2nd return stack item
dec r1
mov dpl,@r1
ret
;Z SP@ -- a-addr get data stack pointer
.drw link
.set link,*+1
.db 0,3,"SP@"
SPFETCH: lcall DUP
mov dph,0xff ; 16-bit pointer P2:R0
mov dpl,r0
ret
;Z SP! a-addr -- set data stack pointer
; Note: only the low 8 bits are affected!
.drw link
.set link,*+1
.db 0,3,"SP!"
SPSTORE: mov r0,dpl ; set stack pointer
ajmp poptos ; get new TOS
;Z RP@ -- a-addr get return stack pointer
.drw link
.set link,*+1
.db 0,3,"RP@"
RPFETCH: dec r0 ; push old TOS
mov @r0,dph
dec r0
mov @r0,dpl
mov dph,#0 ; 16-bit pointer 00:SP
mov dpl,sp
ret
;Z RP! a-addr -- set return stack pointer
; Note: only the low 8 bits are significant!
.drw link
.set link,*+1
.db 0,3,"RP!"
RPSTORE: pop dr3 ; save ret addr in r3:r2
pop dr2
mov sp,dpl ; set new stack pointer
push dr2 ; restore ret addr
push dr3
ajmp poptos ; get new TOS
;X NIP x1 x2 -- x2 per stack diagram
.drw link
.set link,*+1
.db 0,3,"NIP"
NIP: inc r0
inc r0
ret
;X TUCK x1 x2 -- x2 x1 x2 per stack diagram
.drw link
.set link,*+1
.db 0,4,"TUCK"
TUCK: acall SWOP
ajmp OVER
; MEMORY OPERATIONS =============================
;C ! x a-addr -- store cell in Data mem
; Byte order is lo,hi.
.drw link
.set link,*+1
.db 0,1,"!"
STORE: mov a,@r0 ; low byte of X
inc r0
movx @dptr,a
inc dptr
mov a,@r0 ; high byte of X
inc r0
movx @dptr,a
ajmp poptos ; pop new TOS
;C C! c c-addr -- store char in Data mem
.drw link
.set link,*+1
.db 0,2,"C!"
CSTORE: mov a,@r0 ; low byte is char
inc r0
movx @dptr,a
inc r0 ; skip high byte
ajmp poptos ; pop new TOS
;C @ a-addr -- x fetch cell from Data mem
; Byte order is lo,hi.
.drw link
.set link,*+1
.db 0,1,"@"
FETCH: movx a,@dptr ; low byte
mov r2,a ; ..temporary stash
inc dptr
movx a,@dptr ; high byte
mov dpl,r2 ; copy to TOS (DPTR)
mov dph,a
ret
;C C@ c-addr -- c fetch char from Data mem
.drw link
.set link,*+1
.db 0,2,"C@"
CFETCH: movx a,@dptr
mov dpl,a
mov dph,#0
ret
; ARITHMETIC AND LOGICAL OPERATIONS =============
;C FALSE -- false
.drw link
.set link,*+1
.db 0,5,"FALSE"
FALSE: acall DUP
mov dptr,#0
ret
;C TRUE -- true
.drw link
.set link,*+1
.db 0,4,"TRUE"
TRUE : acall DUP
mov dptr,#-1
ret
;C + n1/u1 n2/u2 -- n3/u3 add n1+n2
.drw link
.set link,*+1
.db 0,1,"+"
PLUS: mov a,dpl ; low byte
add a,@r0
inc r0
mov dpl,a
mov a,dph ; high byte
addc a,@r0
inc r0
mov dph,a
ret
;Z M+ d n -- d add single to double
.drw link
.set link,*+1
.db 0,2,"M+"
MPLUS: mov dr2,@r0 ; pop d.high -> r3:r2
inc r0
mov dr3,@r0
inc r0
mov a,@r0 ; d.low, low byte
add a,dpl
mov @r0,a
inc r0
mov a,@r0 ; d.low, high byte
addc a,dph
mov @r0,a
dec r0
clr a
addc a,r2 ; d.high, low byte
mov dpl,a
clr a
addc a,r3 ; d.high, high byte
mov dph,a
ret
;C - n1/u1 n2/u2 -- n3/u3 subtract n1-n2
.drw link
.set link,*+1
.db 0,1,"-"
MINUS: mov a,@r0 ; low byte
inc r0
clr c
subb a,dpl
mov dpl,a
mov a,@r0 ; high byte
inc r0
subb a,dph
mov dph,a
ret
;C AND x1 x2 -- x3 logical AND
.drw link
.set link,*+1
.db 0,3,"AND"
AND: mov a,@r0 ; low byte
inc r0
anl a,dpl
mov dpl,a
mov a,@r0 ; high byte
inc r0
anl a,dph
mov dph,a
ret
;C OR x1 x2 -- x3 logical OR
.drw link
.set link,*+1
.db 0,2,"OR"
OR: mov a,@r0 ; low byte
inc r0
orl a,dpl
mov dpl,a
mov a,@r0 ; high byte
inc r0
orl a,dph
mov dph,a
ret
;C XOR x1 x2 -- x3 logical XOR
.drw link
.set link,*+1
.db 0,3,"XOR"
XOR: mov a,@r0 ; low byte
inc r0
xrl a,dpl
mov dpl,a
mov a,@r0 ; high byte
inc r0
xrl a,dph
mov dph,a
ret
;C INVERT x1 -- x2 bitwise inversion
.drw link
.set link,*+1
.db 0,6,"INVERT"
INVERT: xrl dpl,#0xff
xrl dph,#0xff
ret
;C NEGATE x1 -- x2 two's complement
.drw link
.set link,*+1
.db 0,6,"NEGATE"
NEGATE: xrl dpl,#0xff
xrl dph,#0xff
inc dptr
ret
;C 1+ n1/u1 -- n2/u2 add 1 to TOS
.drw link
.set link,*+1
.db 0,2,"1+"
ONEPLUS: inc dptr
ret
;C 1- n1/u1 -- n2/u2 subtract 1 from TOS
.drw link
.set link,*+1
.db 0,2,"1-"
ONEMINUS: mov a,dpl
jnz dphok
dec dph ; if dpl=0, decr. affects dph
dphok: dec dpl
ret
;Z >< x1 -- x2 swap bytes (not ANSI)
.drw link
.set link,*+1
.db 0,2,"><"
swapbytes: mov a,dpl
mov dpl,dph
mov dph,a
ret
;C 2* x1 -- x2 arithmetic left shift
.drw link
.set link,*+1
.db 0,2,"2*"
TWOSTAR: mov a,dpl ; lo byte, left shift
add a,dpl
mov dpl,a
mov a,dph ; hi byte, left rot w/cy
rlc a
mov dph,a
ret
;C 2/ x1 -- x2 arithmetic right shift
.drw link
.set link,*+1
.db 0,2,"2/"
TWOSLASH: mov a,dph ; get msb of TOS into cy
rlc a
mov a,dph ; high byte, right rotate
rrc a
mov dph,a
mov a,dpl ; low byte, right rotate
rrc a
mov dpl,a
ret
;C LSHIFT x1 u -- x2 logical left shift
.drw link
.set link,*+1
.db 0,6,"LSHIFT"
LSHIFT: mov r4,dpl ; r4 = loop counter
acall DROP
inc r4 ; test for r4=0 case
sjmp lshtest
lshloop: mov a,dpl ; shift left
add a,dpl
mov dpl,a
mov a,dph
rlc a
mov dph,a
lshtest: djnz r4,lshloop
ret
;C RSHIFT x1 u -- x2 logical right shift
.drw link
.set link,*+1
.db 0,6,"RSHIFT"
RSHIFT: mov r4,dpl ; r4 = loop counter
acall DROP
inc r4 ; test for r4=0 case
sjmp rshtest
rshloop: clr c ; clear carry
mov a,dph ; shift right
rrc a
mov dph,a
mov a,dpl
rrc a
mov dpl,a
rshtest: djnz r4,rshloop
ret
;C +! n/u a-addr -- add cell to Data mem
.drw link
.set link,*+1
.db 0,2,"+!"
PLUSSTORE:
movx a,@dptr ; low byte of memory
add a,@r0
inc r0
movx @dptr,a
inc dptr
movx a,@dptr ; high byte of memory
addc a,@r0
inc r0
movx @dptr,a
ajmp poptos ; pop new TOS
; COMPARISON OPERATIONS =========================
;X <> x1 x2 -- flag test not equal
.drw link
.set link,*+1
.db 0,2,"<>"
NOTEQUAL: mov a,@r0
inc r0
cjne a,dpl,NOTEQUAL1
mov a,@r0
inc r0
cjne a,dph,NOTEQUAL2
mov dptr,#0
ret
NOTEQUAL1: inc r0
NOTEQUAL2: mov dptr,#-1
ret
;C 0= n/u -- flag return true if TOS=0
.drw link
.set link,*+1
.db 0,2,"0="
ZEROEQUAL: mov a,dph
zequ1: orl a,dpl ; A = z or nz, per DPTR
jnz is1
mov dptr,#-1
ret
is1:
mov dptr,#0
ret
;C 0< n -- flag true if TOS negative
.drw link
.set link,*+1
.db 0,2,"0<"
ZEROLESS: mov a,dph
rlc a ; cy set if A negative
; propagate cy thru TOS
cyprop: subb a,acc ; -1 if A was 0, else 0
mov dph,a
mov dpl,a
ret ; NB! A=0 iff TOS=0
;C 0> n -- flag true if TOS > 0
.drw link
.set link,*+1
.db 0,2,"0>"
ZEROGREATER: mov a,dpl
add a,#0xff
mov a,dph
addc a,#0xff
sjmp cyprop
;C = x1 x2 -- flag test x1=x2
.drw link
.set link,*+1
.db 0,1,"="
EQUAL: mov a,@r0
inc r0
cjne a,dpl,EQUAL1
mov a,@r0
inc r0
cjne a,dph,EQUAL2
mov dptr,#-1
ret
EQUAL1: inc r0
EQUAL2: mov dptr,#0
ret
;C < n1 n2 -- flag test n1<n2, signed
.drw link
.set link,*+1
.db 0,1,"<"
LESS: acall MINUS ; n1-n2 in TOS, A=DPH,
; CY and OV valid
; if result negative (MSB=1) & not OV, n1<n2
; neg. & OV => n1 +ve, n2 -ve, result -ve, n1>n2
; if result positive (MSB=0) & not OV, n1>=n2
; pos. & OV => n1 -ve, n2 +ve, result +ve, n1<n2
; thus OV reverses the sense of the sign bit
jnb psw.2,msbok ; jump if overflow clear
cpl a ; OV set: invert msb
msbok: rlc a ; put msb (sign) in cy
sjmp cyprop ; & propagate thru TOS
;C > n1 n2 -- flag test n1>n2, signed
.drw link
.set link,*+1
.db 0,1,">"
GREATER: acall SWOP
sjmp LESS
;C U< u1 u2 -- flag test n1<n2, unsigned
.drw link
.set link,*+1
.db 0,2,"U<"
ULESS: mov a,@r0 ; low byte
inc r0
clr c
subb a,dpl
mov a,@r0 ; high byte
inc r0
subb a,dph
sjmp cyprop ; propagate cy thru TOS
;X U> u1 u2 -- flag test u1>u2, unsigned
.drw link
.set link,*+1
.db 0,2,"U>"
; UGREATER: acall SWOP
; sjmp ULESS
UGREATER: mov a,dpl ; low byte
clr c
subb a,@r0
inc r0
mov a,dph ; high byte
subb a,@r0
inc r0
sjmp cyprop ; propagate cy thru TOS
; DOUBLE OPERATORS ==============================
;C 2@ a-addr -- x1 x2 fetch 2 cells
; DUP CELL+ @ SWAP @ ;
; the lower address will appear on top of stack
.drw link
.set link,*+1
.db 0,2,"2@"
TWOFETCH: acall DUP
inc dptr
inc dptr
acall FETCH
acall SWOP
ajmp FETCH
;C 2! x1 x2 a-addr -- store 2 cells
; SWAP OVER ! CELL+ ! ;
; the top of stack is stored at the lower adrs
.drw link
.set link,*+1
.db 0,2,"2!"
TWOSTORE: acall SWOP
acall OVER
acall STORE
inc dptr
inc dptr
ajmp STORE
;C 2DROP x1 x2 -- drop 2 cells
; DROP DROP ;
.drw link
.set link,*+1
.db 0,5,"2DROP"
TWODROP: inc r0
inc r0
ajmp DROP
;C 2DUP x1 x2 -- x1 x2 x1 x2 dup top 2 cells
; OVER OVER ;