Applecorn/applecorn.s
2021-08-19 13:50:59 -04:00

178 lines
4.9 KiB
ArmAsm

* APPLECORN.S
* (c) Bobbi 2021 GPLv3
*
* Load an Acorn BBC Micro ROM in aux memory and
* Provide an environment where it can run
*
* Assembled with the Merlin 8 v2.58 assembler on Apple II.
XC ; 65c02
ORG $2000 ; Load addr of loader in main memory
* Monitor routines
BELL EQU $FBDD
PRBYTE EQU $FDDA
COUT1 EQU $FDED
CROUT EQU $FD8E
HOME EQU $FC58
AUXMOVE EQU $C311
XFER EQU $C314
* Monitor ZP locations
A1L EQU $3C
A1H EQU $3D
A2L EQU $3E
A2H EQU $3F
A4L EQU $42
A4H EQU $43
* Used by XFER
STRTL EQU $3ED
STRTH EQU $3EE
* Reset vector (2 bytes + 1 byte checksum)
RSTV EQU $3F2
* IRQ vector
A2IRQV EQU $3FE
* MLI entry point
MLI EQU $BF00
* IO Buffer for reading file (1024 bytes)
IOBUF0 EQU $4000 ; For loading ROM, OSFILE, *.
IOBUF1 EQU $4400 ; Four open files for langs
IOBUF2 EQU $4800
IOBUF3 EQU $4C00
IOBUF4 EQU $5000
* 512 byte buffer sufficient for one disk block
BLKBUF EQU $5200
BLKBUFEND EQU $5400
* Address in aux memory where ROM will be loaded
AUXADDR EQU $8000
* Address in aux memory where the MOS shim is located
AUXMOS1 EQU $2000 ; Temp staging area in Aux
EAUXMOS1 EQU $4000 ; End of staging area
AUXMOS EQU $D000 ; Final location in aux LC
* Called by code running in main mem to invoke a
* routine in aux memory
XF2AUX MAC
LDX $C08B ; R/W LC RAM, bank 1
LDX $C08B
LDX #<]1
STX STRTL
LDX #>]1
STX STRTH
SEI ; Disable IRQ before XFER
SEC ; Use aux memory
BIT $FF58 ; Set V: use alt ZP and LC
JMP XFER
EOM
* Called by code running in aux mem to invoke a
* routine in main memory
XF2MAIN MAC
LDX STRTL
STX STRTBCKL
LDX STRTH
STX STRTBCKH
LDX #<]1
STX STRTL
LDX #>]1
STX STRTH
SEI ; Disable IRQ before XFER
TSX
STX $0101 ; Save alt SP
LDX $0100 ; Load main SP into X
CLC ; Use main mem
CLV ; Use main ZP and LC
JMP XFER
EOM
* Macro called on re-entry to aux memory
* Careful: This enables IRQ - not for use in ISR
ENTAUX MAC
LDX $0101 ; Recover alt SP
TXS
CLI ; Re-enable IRQ after XFER
LDX STRTBCKL
STX STRTL
LDX STRTBCKH
STX STRTH
EOM
* Macro called on re-entry to main memory
* Careful: This enables IRQ - not for use in ISR
ENTMAIN MAC
TXS ; Main SP already in X
LDX $C081 ; Bank in ROM
LDX $C081
CLI ; Re-enable IRQ after XFER
EOM
* Macro called on re-entry to aux memory
* For use in interrupt handlers (no CLI!)
IENTAUX MAC
LDX $0101 ; Recover alt SP
TXS
LDX STRTBCKL
STX STRTL
LDX STRTBCKH
STX STRTH
EOM
* Macro called on re-entry to main memory
* For use in interrupt handlers (no CLI!)
IENTMAIN MAC
TXS ; Main SP already in X
LDX $C081 ; Bank in ROM
LDX $C081
EOM
* Enable writing to main memory (for code running in aux)
WRTMAIN MAC
SEI ; Keeps IRQ handler easy
STA $C004 ; Write to main memory
EOM
* Go back to writing to aux (for code running in aux)
WRTAUX MAC
STA $C005 ; Write to aux memory
CLI ; Normal service resumed
EOM
* Manually enable AltZP (for code running in main)
ALTZP MAC
SEI ; Disable IRQ when AltZP on
LDA $C08B ; R/W LC bank 1
LDA $C08B
STA $C009 ; Alt ZP and LC
EOM
* Manually disable AltZP (for code running in main)
MAINZP MAC
STA $C008 ; Main ZP and LC
LDA $C081 ; Bank ROM back in
LDA $C081
CLI ; Turn IRQ back on
EOM
* Code is all included from PUT files below ...
* ... order matters!
PUT LOADER
PUT MAIN.ROMMENU
PUT MAINMEM
PUT AUXMEM.MOSEQU
PUT AUXMEM.INIT
PUT AUXMEM.VDU
PUT AUXMEM.HOSTFS
PUT AUXMEM.OSCLI
PUT AUXMEM.BYTWRD
PUT AUXMEM.CHARIO
PUT AUXMEM.MISC