COMMON/common/common.asm
2018-08-07 21:36:06 -04:00

405 lines
7.2 KiB
NASM

#include "rom.h"
#include "common.h"
; ROM code header
.WORD CMN_CD, _END_CMN_CD - CMN_CD
; beginning of ROM code
* = CMN_CD
_CMN .( ; common function interpreter
JSR _SAV ; save registers
PLA
STA _PCL ; set program counter from return address
PLA
STA _PCH
INC _PCL ; advance the program counter
BNE _1
INC _PCH
_1 JSR _2 ; interpret and execute one common instruction
JMP _1
_2 LDY #0
LDA (_PC),Y ; get operand
INC _PCL ; advance the program counter
BNE _3
INC _PCH
_3 TAX ; save operand for later
AND #$F0
BEQ _4 ; go to 0X instructions
CMP #$F0 ; check for FX functions
BEQ _5 ; go to FX instructions
LSR ; get offset to XR instructions
LSR
LSR
TAY
DEY
DEY
LDA FN_XR+1,Y ; push high address
PHA
LDA FN_XR,Y ; push low address
PHA
TXA ; restore operand
AND #$F ; mask to get register
ASL ; shift to get offset to register
ASL
TAX ; back to index
RTS ; "return" to routine
_4 TXA ; get operand
ASL ; shift to get offset to 0X instructions
TAY
LDA FN_0X+1,Y ; push high address
PHA
LDA FN_0X,Y ; push low address
PHA
TXA ; restore operand
RTS ; "return" to routine
_5 TXA ; get operand
AND #$F ; mask to get index
ASL ; shift to get offset to FX instructions
TAY
LDA FN_FX+1,Y ; push high address
PHA
LDA FN_FX,Y ; push low address
PHA
TXA ; restore operand
RTS ; "return" to routine
.)
_INI .( ; initialize common
LDA #0 ; initialize RSI
STA _RSI
; copy system functions (TODO)
; load program (TODO)
JMP (_PC) ; go to last loaded block
.)
_SAV .( ; save the registers prior to entering common
STA _ACC
STX _IDX
STY _IDY
PHP
PLA
STA _PS
CLD
RTS
.)
_RES .( ; restore the registers prior to leaving common
LDA _PS
PHA
LDA _ACC
LDX _IDX
LDY _IDY
PLP
RTS
.)
_SET .( ; SET r aabbcc.dd 1r dd cc bb aa Rr <- aabbcc.dd - set register
LDY #0
LDA (_PC),Y ; transfer four bytes over
STA _R0,X
INY
LDA (_PC),Y
STA _R0+1,X
INY
LDA (_PC),Y
STA _R0+2,X
INY
LDA (_PC),Y
STA _R0+3,X
LDA #4 ; update program counter
CLC
ADC _PCL
STA _PCL
BCC _1
INC _PCH
_1 RTS ; done
.)
_PSH .( ; PSH r 2r RS <- Rr - push onto stack
LDY _RSI ; get register stack index
CPY #_RSS ; compare against limit
BCC _1 ; still room, all okay
BRK ; next push will cause a stack overflow, abort and call exception handler (TODO)
_1 LDA _R0,X ; transfer four bytes over
STA _RS,Y
INY
LDA _R0+1,X
STA _RS,Y
INY
LDA _R0+2,X
STA _RS,Y
INY
LDA _R0+3,X
STA _RS,Y
INY
STY _RSI ; update register stack index
RTS
.)
_POP .( ; POP r 3r Rr <- RS - pop from stack
LDY _RSI ; get register stack index
BNE _1 ; all good, something can be popped off the stack
BRK ; next pop will cause a stack underflow, abort and call exception handler (TODO)
_1 DEY ; transfer four bytes over
LDA _RS,Y
STA _R0+3,X
DEY
LDA _RS,Y
STA _R0+2,X
DEY
LDA _RS,Y
STA _R0+1,X
DEY
LDA _RS,Y
STA _R0,X
STY _RSI ; update register stack index
RTS
.)
_EXC .( ; EXC r 4r Rr <-> RS - exchange Rr with stack
LDY _RSI ; RS to RD
LDA _RS-1,Y
STA _RD+3
LDA _RS-2,Y
STA _RD+2
LDA _RS-3,Y
STA _RD+1
LDA _RS-4,Y
STA _RD
LDA _R0,X ; copy Rr to RS
STA _RS-4,Y
LDA _R0+1,X
STA _RS-3,Y
LDA _R0+2,X
STA _RS-2,Y
LDA _R0+3,X
STA _RS-1,Y
LDA _RD ; copy RD to Rr
STA _R0,X
LDA _RD+1
STA _R0+1,X
LDA _RD+2
STA _R0+2,X
LDA _RD+3
STA _R0+3,X
RTS
.)
_ADDRD .( ; add RD to register indexed by X
LDA _R0+3,X
AND #_MSK_O ; check for existing overflow condition
BEQ _4
EOR #_MSK_O
BNE _3 ; existing overflow, skip decrement operation
_4 CLC ; adding RD
LDA _RD
ADC _R0,X
STA _R0,X
LDA _RD+1
ADC _R0+1,X
STA _R0+1,X
LDA _RD+2
ADC _R0+2,X
STA _R0+2,X
LDA _RD+3
ADC _R0+3,X
STA _R0+3,X
AND #_MSK_O ; check for overflow
BEQ _2
EOR #_MSK_O
BEQ _2
_3 LDA _F ; set overflow
ORA #_F_O
STA _F
BNE _5
_2 LDA _F ; clear overflow
AND #_F_O^$FF
STA _F
_5 RTS
.)
_INR .( ; INR r 5r Rr <- Rr + 1.0 - increment register
LDA #0 ; set RD to plus one
STA _RD
LDA #_PLS_1
STA _RD+1
LDA #0
STA _RD+2
STA _RD+3
BEQ _ADDRD
.)
_DCR .( ; DCR r 6r Rr <- Rr - 1.0 - decrement register
LDA #0 ; set RD to minus one
STA _RD
LDA #_MNS_1
STA _RD+1
LDA #$FF
STA _RD+2
STA _RD+3
BNE _ADDRD
.)
_TST .( ; TST r 7r F <- Rr <=> 0.0 - test register
LDA _F
AND #_MSK_T ; clear TST bits
STA _F
LDA _R0+3,X ; check highest byte
BMI _1 ; is negative
ORA _R0+2,X ; could be positive or zero, OR with all other bytes
ORA _R0+1,X
ORA _R0,X
BNE _2 ; is positive
LDA #_F_Z ; set zero flag
BNE _3
_1 LDA #_F_N ; set negative flag
BNE _3
_2 LDA #_F_P ; set positive flag
_3 ORA _F
STA _F
RTS
.)
_DEC .( ; DEC r 8r Rr <- dec(Rr) - convert Rr from hex aabbcc.dd to decimal ######.##
RTS
.)
_HEX .( ; HEX r 9r Rr <- hex(Rr) - convert Rr from decimal ######.## to hex aabbcc.dd
RTS
.)
_ADD .( ; ADD r pq ar pq Rr <- Rp + Rq - addition
RTS
.)
_SUB .( ; SUB r pq br pq Rr <- Rp - Rq - subtraction
RTS
.)
_MUL .( ; MUL r pq cr pq Rr <- Rp * Rq - multiplication
RTS
.)
_DIV .( ; DIV r pq dr pq Rr <- Rp / Rq - division
RTS
.)
_MOD .( ; MOD r pq er pq Rr <- Rp % Rq - modulus
RTS
.)
_ESC .( ; ESC 00 - escape back into regular assembler
PLA ; discard the COMMON _1 return address
PLA
JSR _RES ; restore the registers
JMP (_PC) ; get back in the code
.)
_RTN .( ; RTN 01 - return from subroutine
RTS
.)
_BRS .( ; BRS xxyy 02 yy xx PC <- PC + xxyy - branch to subroutine
RTS
.)
_BRA .( ; BRA xxyy 03 yy xx PC <- PC + xxyy - branch always
RTS
.)
_BRX .( ; generic branch testing
AND _F ; check the bit
BNE _BRA ; if set, branch
CLC ; not set, advance the program counter over the xxyy offset
LDA #2
ADC _PCL
STA _PCL
LDA #0
ADC _PCH
STA _PCH
RTS
.)
_BRE .( ; BRE xxyy 04 yy xx PC <- PC + xxyy - branch if Rp = Rq (after CMP)
LDA #_F_E
BNE _BRX
.)
_BRG .( ; BRG xxyy 05 yy xx PC <- PC + xxyy - branch if Rp > Rq (after CMP)
LDA #_F_G
BNE _BRX
.)
_BRL .( ; BRL xxyy 06 yy xx PC <- PC + xxyy - branch if Rp < Rq (after CMP)
LDA #_F_L
BNE _BRX
.)
_BRZ .( ; BRZ xxyy 07 yy xx PC <- PC + xxyy - branch if Rr = 0.0 (after TST)
LDA #_F_Z
BNE _BRX
.)
_BRP .( ; BRP xxyy 08 yy xx PC <- PC + xxyy - branch if Rr > 0.0 (after TST)
LDA #_F_P
BNE _BRX
.)
_BRN .( ; BRN xxyy 09 yy xx PC <- PC + xxyy - branch if Rr < 0.0 (after TST)
LDA #_F_N
BNE _BRX
.)
_BRO .( ; BRO xxyy 0a yy xx PC <- PC + xxyy - branch if overflow (after arithmetic operations)
LDA #_F_O
BNE _BRX
.)
_BRU .( ; BRU xxyy 0b yy xx PC <- PC + xxyy - branch if underflow (after arithmetic operations)
LDA #_F_U
BNE _BRX
.)
_CPR .( ; CPR pq 0c pq Rp <- Rq - copy register
RTS
.)
_LDI .( ; LDI pq 0d pq Rp <- (Rq:bbcc) - load indirect from memory
RTS
.)
_SVI .( ; SVI pq 0e pq (Rp:bbcc) <- Rq - save indirect to memory
RTS
.)
_CMR .( ; CMR pq 0f pq F <- Rp <=> Rq - compare registers
RTS
.)
_END_CMN_CD
; ROM data header
.WORD CMN_DT, _END_CMN_DT - CMN_DT
; beginning of ROM data
* = CMN_DT
FN_0X .WORD _ESC-1, _RTN-1, _BRS-1, _BRA-1, _BRE-1, _BRG-1, _BRL-1, _BRZ-1,
.WORD _BRP-1, _BRN-1, _BRO-1, _BRU-1, _CPR-1, _LDI-1, _SVI-1, _CMR-1
FN_XR .WORD _SET-1, _POP-1, _PSH-1, _EXC-1, _INR-1, _DCR-1, _TST-1,
.WORD _DEC-1, _HEX-1, _ADD-1, _SUB-1, _MUL-1, _DIV-1, _MOD-1
_END_CMN_DT
; 6502 addresses
.WORD ADDR, 6
; 6502 NMI, Reset and IRQ
* = $FFFA
ADDR .WORD 0, _INI, 0