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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
SHRSCR1LINE PHY
PHX
STA VDUADDR+1
STZ VDUADDR
PHP
STA VDUADDR+1 ; Screen line -> MSB
STZ VDUADDR+0 ; Zero LSB
PHP ; Disable interrupts
SEI
CLC
CLC ; Enter native mode
XCE
PHB
PHB ; Preserve data bank
REP #$31 ; M,X 16 bit, carry clear
MX %00 ; Tell Merlin
LDA VDUADDR
LDA VDUADDR ; Screen line to scroll
ASL ; Mult 4
ASL
ASL
ADC VDUADDR
ADC VDUADDR ; Mult 5
STA VDUADDR ; VDUADDR = line * $500
LDA TXTWINLFT
ASL
AND #$00ff
ADC VDUADDR
STA VDUADDR ; VDUADDR = Minimum position
LDA TXTWINLFT ; Left margin
ASL ; 2 bytes / char
AND #$00ff ; Mask to get 8 bit result
ADC VDUADDR ; Add to beginning of line addr
STA VDUADDR ; VDUADDR = start position
SEP #$21 ; M 8 bit, X 16 bit, carry set
MX %10 ; Tell Merlin
LDA TXTWINRGT
SBC TXTWINLFT
LDA TXTWINRGT ; Compute width ..
SBC TXTWINLFT ; .. right minus left
REP #$31 ; M,X 16 bit, carry clear
MX %00 ; Tell Merlin
ASL
AND #$00ff
ADC VDUADDR
TAX
PEA #$e1e1
ASL ; 2 bytes / char
AND #$00ff ; Mask to get 8 bit result
ADC VDUADDR ; Add to start position
TAX ; Will use as index
PEA #$e1e1 ; Set databank to $E1
PLB
PLB
:LOOP1 LDA $2500,x ; 2 bytes, row 0
@ -391,15 +391,15 @@ SHRSCR1LINE PHY
STA $23c0,x
LDA $2960,x ; row 7
STa $2460,x
DEX ; Update index
DEX
DEX
BMI :DONE
CPX VDUADDR
BCS :LOOP1
:DONE PLB
SEC
BMI :DONE ; Jump out if odd->-ve
CPX VDUADDR ; Compare with start addr
BCS :LOOP1 ; Bytes left? Go again
:DONE PLB ; Recover data bank
SEC ; Back to emulation mode
XCE
PLP
PLP ; Recover flags + regs
PLX
PLY
RTS