OK OK, here's the kernel code. It's rather long and
repetitive, but I've commented all of the main loop
with the standard Nick Bensema cycle notation. :)
; *****************************
; * DISPLAY KERNEL SUBROUTINE *
; *****************************
DrawScreen
LDA INTIM
BNE DrawScreen
STA WSYNC
STA VBLANK ; Write a '0' to VBLANK to turn the
TIA back on
STA CTRLPF ; Write a '0' to CTRLPF to set normal
mode
STA CXCLR ; Clear collision
registers for this frame
LDY #160
; This is the first (rather minor) display loop. It
handles the first 40 lines of
; the screen - the area before any of the playfield
appears.
SecondaryScanLoop
STA WSYNC
LDA (P1Offset),Y
STA GRP0
LDA (P2Offset),Y
STA GRP1
DEY
CPY #120
BNE SecondaryScanLoop
; This is the beginning of the primary display loop.
Each iteration handles
; eight lines of the display. 15 iterations are
made, for a total of 120 lines
; of the display.
; The loop had to be unrolled into eight line
segments in order to have
; enough time to draw the playfield as well as load
the data for both players.
; One constraint is this: When the player fires,
the display becomes interlaced.
; Every even numbered screen frame, the players are
displayed, and every odd
; frame, the missile - actually a player object too
- is displayed. Making
; the missile a player object as well means we can
use the same display kernel
; for both types of frames.
LDX #0
LDA PField1A,X ;[58-60]+4
ScanLoop
; ****** FIRST LINE ******
STA WSYNC
STA PF1 ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
STA PF1 ;[64-66]+3
LDA BKColor,X ;4
; ****** SECOND LINE ******
STA WSYNC
STA COLUBK ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
; ****** THIRD LINE ******
STA WSYNC
STA PF1 ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
; ****** FOURTH LINE ******
STA WSYNC
STA PF1 ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
STA PF1 ;[64-66]+3
LDA PFColor,X ;4
; ****** FIFTH LINE ******
STA WSYNC
STA COLUPF ;[0]+3
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
; ****** SIXTH LINE ******
STA WSYNC
STA PF1 ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
; ****** SEVENTH LINE ******
STA WSYNC
STA PF1 ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
LDA PField1A,X ;[58-60]+4
DEY ;[62-64]+2 = 64-66
; ****** EIGHTH LINE ******
STA WSYNC
STA PF1 ;[0]+3 = 3 < 29
; Load player 1 data
LDA (P1Offset),Y ;[3]+5-6
STA GRP0 ;[8-9]+3
; This part loads the playfield data into the PF
registers.
LDA PField0,X ;[11-12]+4
STA PF0 ;[15-16]+3 = 18-19 < 23
ASL ;[18-19]+2
ASL ;[20-21]+2
ASL ;[22-23]+2
ASL ;[24-25]+2
STA PF0 ;[26-27]+3 = 29-30 < 51 and 29-30 >= 29
LDA PField2A,X ;[29-30]+4
STA PF2 ;[33-34]+3 = 36-37 < 40
; Load player 2 data
LDA (P2Offset),Y ;[36-37]+5-6
STA GRP1 ;[41-43]+3
LDA PField1B,X ;[44-46]+4
STA PF1 ;[48-50]+3 = 51-53 < 57 and 51-53 > 40
LDA PField2B,X ;[51-53]+4
STA PF2 ;[55-57]+3 = 58-60 < 68 and 58-60 > 51
INX ;[58-60]+2
LDA PField1A,X ;[60-62]+4
DEY ;[64-66]+2
BEQ Bypass ;[66-68]+2 (if not taken)
JMP ScanLoop ;[68-70]+3 = 71-73 cycles (whew!)
Bypass
; This is the end of the main display loop. Now we
need to clear the playfield
; and playfield registers and reset the first
player graphic to get ready to
; display the 31 lines which comprise the
alphanumerical status area at the
; bottom of the screen.
STA WSYNC
LDA #0
STA GRP0
STA GRP1
STA PF0
STA PF1
STA PF2
LDA #$00
STA COLUBK
STA REFP1
LDA #$12
STA COLUPF
LDA #%00000001
STA NUSIZ0
STA NUSIZ1
; Get score digit memory offset values
LDA P1Health
AND #15
TAX
LDA DigitLookup,X
STA TempAddr2
LDA P1Health
STA RESP0
STA RESP1
LSR
LSR
LSR
LSR
TAX
LDA DigitLookup,X
STA TempAddr1
LDA P2Health
AND #15
TAX
LDA DigitLookup,X
STA TempAddr4
LDA P2Health
LSR
LSR
LSR
LSR
TAX
LDA DigitLookup,X
STA TempAddr3
; Here are the final display loops - they handle the
alphanumerical status area
; at the bottom of the screen
; Draw the player health meters
LDY #7 ;[82]+4
Bottom1
STA WSYNC
LDA #$0F
;LDA #%00110010 ;[0]+2
STA COLUP0 ;[2]+3
STA COLUP1 ;[5]+3
LDA (TempAddr1),Y ;[8]+5
STA GRP0 ;[12]+3
LDA (TempAddr2),Y ;[15]+5
STA GRP1 ;[20]+3
STA RESP0 ;[23]+3
STA RESP1 ;[26]+3
LDA (TempAddr3),Y ;[29]+5
STA GRP0 ;[34]+3
LDA (TempAddr4),Y ;[37]+5
STA GRP1 ;[42]+3
LDA #%11000110 ;[45]+2
NOP ;[47]+2
STA RESP0 ;[49]+3
STA RESP1 ;[52]+3
STA COLUP0 ;[55]+3
STA COLUP1 ;[58]+3
DEY ;[61]+2
CPY #-1 ;[63]+2
BNE Bottom1 ;[65]+3 = 68 (if taken)
; Now we need to set things up to get ready to
display the 'E P W' line
LDA #0
STA GRP0
STA GRP1
STA WSYNC
LDA #%00000001
STA CTRLPF
LDA #%00001111
STA PF1
LDA #%11111111
STA PF2
STA WSYNC
LDA #%00000110
STA NUSIZ0
LDA #%00001000
STA PF1
LDA #0
STA PF2
LDA #$1F
TAX
NOP
NOP
NOP
NOP
NOP
NOP
NOP
STA RESP0
LDY #7
Bottom2
STX COLUP0
STA WSYNC
LDA LetterE,Y ;[]+5
STA GRP0 ;[]+3
DEX
DEX
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
LDA LetterP,Y ;[]+5
STA GRP0 ;[]+3
NOP
NOP
NOP
LDA LetterW,Y ;[]+5
STA GRP0 ;[]+3
DEY ;[]+2
CPY #-1 ;[]+2
BNE Bottom2
STA WSYNC
LDA #%00000110
STA NUSIZ1
LDA #0
STA GRP0
STA GRP1
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
STA RESP0
STA RESP1
; Get score digit memory offset values
LDA Status
AND #%00000001 ; Get current player's turn
BNE DisplayP2Elevation
LDA P1Elevation
JMP EndDisplayP2Elevation
DisplayP2Elevation
LDA P2Elevation
EndDisplayP2Elevation
AND #15
TAX
LDA DigitLookup,X
STA TempAddr2
LDA P1Elevation
LSR
LSR
LSR
LSR
TAX
LDA DigitLookup,X
STA TempAddr1
LDA Status
AND #00000001
BNE DisplayP2Power
LDA P1Power
JMP EndDisplayP2Power
DisplayP2Power
LDA P2Power
EndDisplayP2Power
AND #15
TAX
LDA DigitLookup,X
STA TempAddr4
LDA P1Power
LSR
LSR
LSR
LSR
TAX
LDA DigitLookup,X
STA TempAddr3
LDA Wind
AND #15
TAX
LDA DigitLookup,X
STA TempAddr6
LDA Wind
LSR
LSR
LSR
LSR
TAX
LDA DigitLookup,X
STA TempAddr5
LDY #7
LDA #$04
STA COLUP0
STA COLUP1
Bottom3
STA WSYNC
LDA (TempAddr1),Y ;[]+5
STA GRP0 ;[]+3
LDA (TempAddr2),Y
STA GRP1
NOP
NOP
NOP
NOP
LDA (TempAddr6),Y
TAX
LDA (TempAddr3),Y
STA GRP0
LDA (TempAddr4),Y
STA GRP1
LDA (TempAddr5),Y
STA GRP0
STX GRP1
DEY
CPY #-1 ;[]+2
BNE Bottom3
; Take care of the final two lines
STA WSYNC
LDA #%00001111
STA PF1
LDA #%11111111
STA PF2
LDY #0
STY GRP0
STY GRP1
STA WSYNC
LDA #%00000000
STA PF0
STA PF1
STA PF2
STA CTRLPF
LDA #%00000010
STA VBLANK ; Make TIA output invisible, also
disable joystick latches
; Now we need to worry about it bleeding when we
turn
; the TIA output back on.
; Y is still zero.
STY PF0
STY PF1
STY PF1
STY GRP0
STY GRP1
STY ENAM0
STY ENAM1
STY ENABL
LDY BKColor
STY COLUBK
LDY PFColor
STY COLUPF
RTS
There's basically zero RAM left, also. I'll post the
entire program here soon (later tonight maybe), but
I'm kinda in a hurry right now...
Later,
Ben
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