Applecorn/auxmem.init.s
2021-08-14 02:16:58 -04:00

141 lines
4.1 KiB
ArmAsm

***********************************************************
* BBC Micro 'virtual machine' in Apple //e aux memory
***********************************************************
ZP1 EQU $90 ; $90-$9f are Econet space
; so safe to use
ZP2 EQU $92
ZP3 EQU $94
ROW EQU $96 ; Cursor row
COL EQU $97 ; Cursor column
STRTBCKL EQU $9D
STRTBCKH EQU $9E
MOSSHIM
ORG AUXMOS ; MOS shim implementation
*
* Shim code to service Acorn MOS entry points using
* Apple II monitor routines
* This code is initially loaded into aux mem at AUXMOS1
* Then relocated into aux LC at AUXMOS by MOSINIT
*
* Initially executing at $3000 until copied to $D000
MOSINIT LDX #$FF ; Initialize Alt SP to $1FF
TXS
STA $C005 ; Make sure we are writing aux
STA $C000 ; Make sure 80STORE is off
LDA $C08B ; LC RAM Rd/Wt, 1st 4K bank
LDA $C08B
:MODBRA BRA :RELOC ; NOPped out on first run
BRA :NORELOC
LDA #$EA ; NOP opcode
STA :MODBRA
STA :MODBRA+1
:RELOC LDA #<AUXMOS1 ; Relocate MOS shim
STA A1L
LDA #>AUXMOS1
STA A1H
LDA #<EAUXMOS1
STA A2L
LDA #>EAUXMOS1
STA A2H
LDA #<AUXMOS
STA A4L
LDA #>AUXMOS
STA A4H
:L1 LDA (A1L)
STA (A4L)
LDA A1H
CMP A2H
BNE :S1
LDA A1L
CMP A2L
BNE :S1
BRA :S4
:S1 INC A1L
BNE :S2
INC A1H
:S2 INC A4L
BNE :S3
INC A4H
:S3 BRA :L1
:S4 LDA #<MOSVEC-MOSINIT+AUXMOS1
STA A1L
LDA #>MOSVEC-MOSINIT+AUXMOS1
STA A1H
LDA #<MOSVEND-MOSINIT+AUXMOS1
STA A2L
LDA #>MOSVEND-MOSINIT+AUXMOS1
STA A2H
LDA #<MOSAPI
STA A4L
LDA #>MOSAPI
STA A4H
:L2 LDA (A1L)
STA (A4L)
LDA A1H
CMP A2H
BNE :S5
LDA A1L
CMP A2L
BNE :S5
BRA :S8
:S5 INC A1L
BNE :S6
INC A1H
:S6 INC A4L
BNE :S7
INC A4H
:S7 BRA :L2
:NORELOC ; We should jump up into high memory here
:S8 STA $C00D ; 80 col on
STA $C003 ; Alt charset off
STA $C055 ; PAGE2
LDX #$FF
TXS ; Initialise stack
INX ; X=$00
TXA
:SCLR STA $0000,X ; Clear Kernel memory
STA $0200,X
STA $0300,X
INX
BNE :SCLR
LDX #ENDVEC-DEFVEC-1
:INITPG2 LDA DEFVEC,X ; Set up vectors
STA $200,X
DEX
BPL :INITPG2
JSR CLEAR ; Initialise VDU driver
LDA #<:HELLO
LDY #>:HELLO
JSR PRSTR
LDA #$09 ; Print language name at $8009
LDY #$80
JSR PRSTR
JSR OSNEWL
JSR OSNEWL
CLC ; CLC=Entered from RESET
LDA #$01 ; $01=Entering application code
JMP AUXADDR ; Start Acorn ROM
* No return
:HELLO ASC 'Applecorn MOS v0.01'
DB $0D,$0D,$00