6502
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COMMON
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COMMON/common/common.h

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#ifndef __COMMON_H
#define __COMMON_H
; Using four byte quantities aabbccdd with sign bit, overflow bit, 20 bits significand, 10 bits
; fraction. The quantity is valid if the overflow bit agrees with the sign bit. The intent is
; to be able to recognize an overflow/underflow situation, rescale the arguments, and repeat the
; calculation.
; Largest value: +1048575.999(5) internally $3fffffff
; Smallest value: -1048576.000(0) internally $c0000000
; Plus one: +1 internally $00000400
; Zero: 0 internally $00000000
; Minus one: -1 internally $fffffc00
;
; Literals can be in bases 10, 16, 8, or 2, with $, &, and % as prefixes for bases 16, 8, and 2
; respectively. Some examples, all representing the same value:
;
; DEC: 1000.25
; HEX: $3E8.40
; OCT: &1750.20
; BIN: %1111101000.01
; Instructions
; SET r aabbccdd 1r dd cc bb aa Rr <- aabbccdd - set register
; LDD r xxyy 2r yy xx Rr <- (xxyy) - load register directly from address
; SVD r xxyy 3r yy xx (xxyy) <- Rr - save register directly to address
; PSH r 4r RS <- Rr - push onto stack
; POP r 5r Rr <- RS - pop from stack
; EXC r 6r Rr <-> RS - exchange Rr with stack
; INR r 7r Rr <- Rr + 1.0 - increment register
; DCR r 8r Rr <- Rr - 1.0 - decrement register
; TST r 9r F <- Rr <=> 0.0 - test register
; ADD r pq ar pq Rr <- Rp + Rq - addition
; SUB r pq br pq Rr <- Rp - Rq - subtraction
; MUL r pq cr pq Rr <- Rp * Rq - multiplication
; DIV r pq dr pq Rr <- Rp / Rq - division
; MOD r pq er pq Rr <- Rp % Rq - modulus
; EXT z ... fz ... - system and user defined functions
; ESC 00 - escape back into regular assembler
; RTN 01 - return from subroutine
; BRS xxyy 02 yy xx PC <- PC + xxyy - branch to subroutine
; BRA xxyy 03 yy xx PC <- PC + xxyy - branch always
; BRE xxyy 04 yy xx PC <- PC + xxyy - branch if Rp = Rq (after CMR)
; BRG xxyy 05 yy xx PC <- PC + xxyy - branch if Rp > Rq (after CMR)
; BRL xxyy 06 yy xx PC <- PC + xxyy - branch if Rp < Rq (after CMR)
; BRZ xxyy 07 yy xx PC <- PC + xxyy - branch if Rr = 0.0 (after TST)
; BRP xxyy 08 yy xx PC <- PC + xxyy - branch if Rr > 0.0 (after TST)
; BRN xxyy 09 yy xx PC <- PC + xxyy - branch if Rr < 0.0 (after TST)
; BRO xxyy 0a yy xx PC <- PC + xxyy - branch if overflow (after arithmetic operations)
; BRU xxyy 0b yy xx PC <- PC + xxyy - branch if underflow (after arithmetic operations)
; CPR pq 0c pq Rp <- Rq - copy register
; LDI pq 0d pq Rp <- (int(Rq)) - load indirect via index to allocated memory (offset = index * 4)
; SVI pq 0e pq (int(Rp)) <- Rq - save indirect via index to allocated memory (offset = index * 4)
; CMR pq 0f pq F <- Rp <=> Rq - compare registers
; 40 bytes in page zero for common registers
_R0 = $100 - 4 * (10 + 10)
_R1 = _R0 + 4
_R2 = _R1 + 4
_R3 = _R2 + 4
_R4 = _R3 + 4
_R5 = _R4 + 4
_R6 = _R5 + 4
_R7 = _R6 + 4
_R8 = _R7 + 4
_R9 = _R8 + 4
; 40 bytes in page zero for internal registers
_I0 = _R9 + 4 ; workspace
_I1 = _I0 + 4
_I2 = _I1 + 4
_I3 = _I2 + 4
_I4 = _I3 + 4
_I5 = _I4 + 4
_I6 = _I5 + 4 ; register I6 maintains common status
_I7 = _I6 + 4 ; register I7 maintains locations of code and allocated memory
_I8 = _I7 + 4 ; register I8 is reserved for future use, e.g. context switching
_I9 = _I8 + 4 ; register I9 saves/restores processor status
; register I6 maintains common status
; (dd cc bb aa) aa: index for register stack RS / ccbb: program counter PC / dd: flags F UONPZLGE
_RSI = _I6 ; register stack index
_PCL = _RSI + 1 ; program counter low
_PCH = _PCL + 1 ; program counter high
_F = _PCH + 1 ; flags
_PC = _PCL ; program counter
; bits for flags
_F_E = 1 ; if Rp = Rq (after CMP)
_F_G = 2 ; if Rp > Rq (after CMP)
_F_L = 4 ; if Rp < Rq (after CMP)
_F_Z = 8 ; if Rr = 0.0 (after TST)
_F_P = 16 ; if Rr > 0.0 (after TST)
_F_N = 32 ; if Rr < 0.0 (after TST)
_F_O = 64 ; if overflow (after arithmetic operations)
_F_U = 128 ; if underflow (after arithmetic operations)
; register I7 maintains locations of allocated memory
_ARLL = _I7 ; allocated low and high bytes
_ARLH = _ARLL + 1
_ARUL = _ARLH + 1 ; allocated upper limit
_ARUH = _ARUL + 1
_AR = _ARLL ; allocated memory address
; register I8 is reserved for future use, e.g. context switching
; register I9 saves/restores processor status
; (dd cc bb aa) aa: accumulator, bb: index X, cc: index Y, dd: processor status
_ACC = _I9 ; saved accumulator to restore
_IDX = _ACC + 1 ; saved index X to restore
_IDY = _IDX + 1 ; saved index Y to restore
_PS = _IDY + 1 ; saved processor status to restore
; 6502 stack resides on page one
; using some of page two for register stack
_RS = $200 ; register stack
_RSS = FN_FX - _RS ; register stack size
; system & user functions
; 32 bytes at the end of page two
FN_FX = $300 - 2 * 16 ; list of system and user functions
; function constants
_ESC_C = $00
_RTN_C = $01
_BRS_C = $02
_BRA_C = $03
_BRE_C = $04
_BRG_C = $05
_BRL_C = $06
_BRZ_C = $07
_BRP_C = $08
_BRN_C = $09
_BRO_C = $0a
_BRU_C = $0b
_CPR_C = $0c
_LDI_C = $0d
_SVI_C = $0e
_CMR_C = $0f
_SET_C = $10
_LDD_C = $20
_SVD_C = $30
_PSH_C = $40
_POP_C = $50
_EXC_C = $60
_INR_C = $70
_DCR_C = $80
_TST_C = $90
_ADD_C = $a0
_SUB_C = $b0
_MUL_C = $c0
_DIV_C = $d0
_MOD_C = $e0
_EXT_C = $f0
; common constants
_MSK_O = %11000000 ; mask for overflow
_MSK_R = %00111100 ; mask for registers
_MSK_T = (_F_Z + _F_P + _F_N) ^ $ff ; mask for TST
_MSK_C = (_F_E + _F_G + _F_L) ^ $ff ; mask for CMP
; section modifiers
_SM_FXD = %00000001
_SM_RLC = %00000010
_SM_CD = %00000100
_SM_DT = %00001000
; section identifiers
_RLC_CD = _SM_RLC + _SM_CD ; relocatable code
_RLC_DT = _SM_RLC + _SM_DT ; relocatable data
#endif /* __COMMON_H */
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