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Added comments to Kent's code.

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Bobbi Webber-Manners 2022-12-26 22:42:31 -05:00
parent 1a2d98bec4
commit 19a8842b5f
2 changed files with 27 additions and 27 deletions
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applecorn.po
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54
auxmem.shr.s
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@ -343,36 +343,36 @@ SHRNEXTROW LDA VDUADDR+0 ; Add 160 to VDUADDR
* TODO: This is only for 640 mode at present * TODO: This is only for 640 mode at present
SHRSCR1LINE PHY SHRSCR1LINE PHY
PHX PHX
STA VDUADDR+1 STA VDUADDR+1 ; Screen line -> MSB
STZ VDUADDR STZ VDUADDR+0 ; Zero LSB
PHP PHP ; Disable interrupts
SEI SEI
CLC CLC ; Enter native mode
XCE XCE
PHB PHB ; Preserve data bank
REP #$31 ; M,X 16 bit, carry clear REP #$31 ; M,X 16 bit, carry clear
MX %00 ; Tell Merlin MX %00 ; Tell Merlin
LDA VDUADDR LDA VDUADDR ; Screen line to scroll
ASL ; Mult 4
ASL ASL
ASL ADC VDUADDR ; Mult 5
ADC VDUADDR
STA VDUADDR ; VDUADDR = line * $500 STA VDUADDR ; VDUADDR = line * $500
LDA TXTWINLFT LDA TXTWINLFT ; Left margin
ASL ASL ; 2 bytes / char
AND #$00ff AND #$00ff ; Mask to get 8 bit result
ADC VDUADDR ADC VDUADDR ; Add to beginning of line addr
STA VDUADDR ; VDUADDR = Minimum position STA VDUADDR ; VDUADDR = start position
SEP #$21 ; M 8 bit, X 16 bit, carry set SEP #$21 ; M 8 bit, X 16 bit, carry set
MX %10 ; Tell Merlin MX %10 ; Tell Merlin
LDA TXTWINRGT LDA TXTWINRGT ; Compute width ..
SBC TXTWINLFT SBC TXTWINLFT ; .. right minus left
REP #$31 ; M,X 16 bit, carry clear REP #$31 ; M,X 16 bit, carry clear
MX %00 ; Tell Merlin MX %00 ; Tell Merlin
ASL ASL ; 2 bytes / char
AND #$00ff AND #$00ff ; Mask to get 8 bit result
ADC VDUADDR ADC VDUADDR ; Add to start position
TAX TAX ; Will use as index
PEA #$e1e1 PEA #$e1e1 ; Set databank to $E1
PLB PLB
PLB PLB
:LOOP1 LDA $2500,x ; 2 bytes, row 0 :LOOP1 LDA $2500,x ; 2 bytes, row 0
@ -391,15 +391,15 @@ SHRSCR1LINE PHY
STA $23c0,x STA $23c0,x
LDA $2960,x ; row 7 LDA $2960,x ; row 7
STa $2460,x STa $2460,x
DEX ; Update index
DEX DEX
DEX BMI :DONE ; Jump out if odd->-ve
BMI :DONE CPX VDUADDR ; Compare with start addr
CPX VDUADDR BCS :LOOP1 ; Bytes left? Go again
BCS :LOOP1 :DONE PLB ; Recover data bank
:DONE PLB SEC ; Back to emulation mode
SEC
XCE XCE
PLP PLP ; Recover flags + regs
PLX PLX
PLY PLY
RTS RTS