Posted By
JamesD
on 2017-11-28
20:36:48
|  Re: Patch for BASIC to make it faster?
I was running some benchmarks and the horribly slow times indicated it was doing just what it's doing. Way too much to read a byte.
FWIW, the CHARGET and CHARGOT can be patched without doing anything to the ROM.
Just replace the code with the patched version that removes the interrupt disable, switch in RAM, and then switches in ROM, and enables interrupts after reading 1 byte.
But you can't do it from BASIC.
You also need to patch the pointers to the top of memory and things like that, but it's not difficult code.
This is the section of ROM. The disassembly is pretty incomplete so I don't know if you can patch get under ROM or not. I'm not sure what uses it.
The functions are at the following addresses in RAM.
CHRGET equ $0473 ; get byte from basic ( incs LastBasicLineNo first )
CHRGOT equ $0479 ; gets current byte from basic (doesn't inc LastBasicLineNo )
----------------------------------------------------------------------------------------------------------
;
; CHRGET/CHRGOT - This chunk of code is copied to RAM
; and run from there. It is used to get data UNDER the
; system ROM's for basic.
;
; CHRGET ($0473)
L8123 INC LastBasicLineNo ; $3b (goes to $0473 ) CHRGET
BNE L8129
INC LastBasicLineNo+1 ; $3c
;
; CHRGOT ($0479)
;
L8129 SEI <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
STA RAM_ON <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
LDY #$00
LDA (LastBasicLineNo),y ; $3b
STA ROM_ON <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
CLI <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
CMP #$3A ; ":" (colon)
BCS L8143 ; if colon, exit
CMP #$20 ; " " (space)
BEQ L8123 ; if space, get NEXT byte from basic
SEC
SBC #$30
SEC
SBC #$D0
L8143 RTS
L0494 STA $049C ; set location to get byte from.
;
; This section gets copied to $04A5
;
GetUnderROM
SEI ; IRQ's off <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
STA RAM_ON ; DISABLE ROM <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
LDA ($00),y ; get byte ($00 is at location $49C)
STA ROM_ON ; enable ROM <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
CLI ; IRQ's on again.. <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
RTS ; and return...
db $00,$00,$00
-------------------------------------------------------------------------------------------------------------
Rough code for the patch. Unfinished.
SEI
;Set up new pointers here
;copy new CHARGOT routine over old one
LDX #21 ; Copy down NEWCHRGOT
L804C LDA NEWCHARGOT,x ; routines. These are used for
STA $0479,x ; fetching data under the system
DEX ; ROM
BNE L804C
CLI
;return to BASIC here.
ORG $0479 ;assemble for target address, then db the resulting bytes as part of above program
;
; CHRGOT ($0479)
;
NEWCHARGOT
LDY #$00
LDA (LastBasicLineNo),y ; $3b
CMP #$3A ; ":" (colon)
BCS EXIT ; if colon, exit
CMP #$20 ; " " (space)
BEQ $0473 ; if space, get NEXT byte from basic
SEC
SBC #$30
SEC
SBC #$D0
EXIT
RTS
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