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Post by jmpff3d on Nov 10, 2018 20:21:35 GMT
;
;===============================================================================
;
; Commodore 128 - 8722 MEMORY MANAGEMENT UNIT
;
mmu =$d500 ;configuration reg in I/O block
mmuhi =$ff00 ;configuration reg in hi RAM
;
;
mmucr =mmuhi ;configuration...
;
; 7 6 54 32 1 0
;----------------
; 0 x xx xx x x
; | || || | |
; | || || | +---> $D000-$DFFF: 0 = I/O hardware
; | || || | 1 = RAM or character ROM
; | || || +----> $4000-$7FFF: 0 = system ROM
; | || || 1 = RAM
; | || ++-----> $8000-$BFFF: 00 = system ROM
; | || 01 = internal function ROM
; | || 10 = external function ROM
; | || 11 = RAM
; | ++-------> $C000-$FFFF: 00 = system ROM
; | 01 = internal function ROM
; | 10 = external function ROM
; | 11 = RAM
; +---------> RAM bank: 0 = RAM-0
; 1 = RAM-1
;
pcra =mmu+1 ;preconfiguration A
pcrb =mmu+2 ;preconfiguration B
pcrc =mmu+3 ;preconfiguration C
pcrd =mmu+4 ;preconfiguration D
;
;
mmumcr =mmu+5 ;mode configuration...
;
; 7 6 5 4 3 21 0
;-----------------
; x x x x x 00 x
; | | | | | |
; | | | | | +---> active MPU: 0 = Z80
; | | | | | 1 = 8502
; | | | | +------> FSDIR (fast serial control)
; | | | +-------> /GAME
; | | +--------> /EXROM
; | +---------> ROM select: 0 = C-128
; | 1 = C-64
; +----------> 40/80 key: 0 = 80 (down)
; 1 = 40 (up)
;
;
mmurcr =mmu+6 ;memory map configuration...
;
; 7 6 54 32 10
;---------------
; 0 x 00 xx xx
; | || ||
; | || ++---> common RAM size: 00 = 1K
; | || 01 = 4K
; | || 10 = 8K
; | || 11 = 16K
; | ++-----> common RAM area: 00 = none
; | 01 = bottom
; | 10 = top
; | 11 = both
; +---------> VIC video bank: 0 = RAM-0
; 1 = RAM-1
;
mmup0l =mmu+7 ;virtual zero page location
mmup0h =mmu+8 ;virtual zero page RAM bank
mmup1l =mmu+9 ;virtual MPU stack location
mmup1h =mmu+10 ;virtual MPU stack RAM bank
;
lcra =mmucr+1 ;select configuration A
lcrb =mmucr+2 ;select configuration B
lcrc =mmucr+3 ;select configuration C
lcrd =mmucr+4 ;select configuration D
;
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Post by jmpff3d on Nov 11, 2018 23:07:21 GMT
Sample code, related to MMU BitSwitching ...
; "proof of mmu banking" is by #$00 written to ram at $d020/21 without causing change of screen color
; visible in 128 ml monitor -- use .. m 1d020
;
; redirecting zp and stack (and back again) to show it can be done while the system is running
; the relocated stack is unfortunately not directly visible through ml monitor, after you return to normal stack
. 12000 78 sei
. 12001 a9 7f lda #$7f ; sets up alt ramblock with "bank1" config
. 12003 8d 00 ff sta $ff00 ; mmu config register mirror
. 12006 a2 01 ldx #$01
. 12008 8e 0a d5 stx $d50a ; sets stack to alt ramblock (1) .. required
. 1200b 8e 09 d5 stx $d509 ; sets stack to page one .. (not needed here, only for formality)
. 1200e 8e 08 d5 stx $d508 ; sets zp to alt ramblock (1) .. required
. 12011 ca dex
. 12012 8e 07 d5 stx $d507 ; sets zp to page 0 .. (not needed here, only for formality)
. 12015 49 7f eor #$7f ; zeros out A
. 12017 8d 06 d5 sta $d506 ; 0 to $d506 mmu ram config for all ram access to alt ramblock, no i/o
. 1201a a0 04 ldy #$04
. 1201c 8d 20 d0 sta $d020 ; hits here should -NOT- cause visible screen display changes
. 1201f 99 04 01 sta $0104,y ; tiny test fill of stack now at alt-ramblock
; c128 BASIC/Monitor will still poll from zp/stack, if you allow it
. 12022 88 dey
. 12023 d0 f7 bne $201c
. 12025 8e 20 d0 stx $d020 ; hits here should -NOT- cause visible screen display changes
. 12028 8c 20 d0 sty $d020 ; " "
. 1202b 8c 21 d0 sty $d021 ; " "
. 1202e 8c 0a d5 sty $d50a ; sets stack to normal ramblock (0) .. required
. 12031 8c 08 d5 sty $d508 ; sets zp to normal ramblock (0) .. required
. 12034 88 dey
. 12035 8c 00 ff sty $ff00 ; mmu config register back to "bank0" config
. 12038 a9 04 lda #$04 ; mmu ram config back to normal
. 1203a 8d 06 d5 sta $d506
. 1203d 58 cli
. 1203e 60 rts
; you can paste these bytes below into emulated machine @ ml monitor, for quick testing of the above code
>12000 78 a9 7f 8d 00 ff a2 01
>12008 8e 0a d5 8e 09 d5 8e 08
>12010 d5 ca 8e 07 d5 49 7f 8d
>12018 06 d5 a0 04 8d 20 d0 99
>12020 04 01 88 d0 f7 8e 20 d0
>12028 8c 20 d0 8c 21 d0 8c 0a
>12030 d5 8c 08 d5 88 8c 00 ff
>12038 a9 04 8d 06 d5 58 60 ff
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