base:horizontal_screen_positioning_hsp
Horizontal Screen Positioning (HSP) aka Wanker aka DMA-Delay
- demo world records and world firsts mentions VSP+IK - there VSP is “Variable Screen Positioning” = DMA Delay = horizontal positioning.
- Also discussed in these posts:
- 2008 thread on CSDB called it HSP/DMA Delay: https://csdb.dk/forums/?roomid=11&topicid=53517&showallposts=1
- VIC Article: 3.14.6. DMA delay : https://www.cebix.net/VIC-Article.txt
This code is for PAL machines. To make it work for NTSC you have to do some minor timing modifications for each scan-line.
The code is in ACME assembler format.
; This demonstrates HSP (Horizontal Screen Positioning) using a stable raster. ; If you have any questions contact the author Martin Piper through CodeBase64 !to "RasterTest.prg", cbm !cpu 6510 !ct pet ZPProcessorPortDDR = $00 ProcessorPortDDRDefault = %101111 ZPProcessorPort = $01 ProcessorPortAllRAMWithIO = %100101 CIA1InterruptControl = $dc0d CIA1TimerAControl = $dc0e CIA1TimerBControl = $dc0f CIA2InterruptControl = $dd0d CIA2TimerAControl = $dd0e CIA2TimerBControl = $dd0f VIC2InteruptControl = $d01a VIC2InteruptStatus = $d019 VIC2BorderColour = $d020 VIC2ScreenColour = $d021 VIC2ScreenControlV = $d011 VIC2SpriteEnable = $d015 VIC2Raster = $d012 CIA1KeyboardColumnJoystickA = $dc00 KERNALNMIServiceRoutineLo = $fffa KERNALNMIServiceRoutineHi = $fffb KERNALIRQServiceRoutineLo = $fffe KERNALIRQServiceRoutineHi = $ffff !macro MACROAckRasterIRQ_A { lda #1 sta VIC2InteruptStatus ; Ack Raster interupt } !macro MACROAckAllIRQs_A { ; Ack any interrupts that might have happened from the CIAs lda CIA1InterruptControl lda CIA2InterruptControl ; Ack any interrupts that have happened from the VIC2 lda #$ff sta VIC2InteruptStatus } *= $0801 !byte $0b,$08,$01,$00,$9e ; Line 1 SYS2061 !convtab pet !tx "2061" ; Address for sys start in text !byte $00,$00,$00 !zn .theLine = 45 ; Stop interrupts, clear decimal mode and backup the previous stack entries sei cld ; Grab everything on the stack ldx #$ff txs ; Init the processor port ldx #ProcessorPortDDRDefault stx ZPProcessorPortDDR ; Set the user requested ROM state ldy #ProcessorPortAllRAMWithIO sty ZPProcessorPort ; Clear all CIA to known state, interrupts off. lda #$7f sta CIA1InterruptControl sta CIA2InterruptControl lda #0 sta VIC2InteruptControl sta CIA1TimerAControl sta CIA1TimerBControl sta CIA2TimerAControl sta CIA2TimerBControl +MACROAckAllIRQs_A ; Setup kernal and user mode IRQ vectors to point to a blank routine lda #<.initIRQ sta KERNALIRQServiceRoutineLo lda #>.initIRQ sta KERNALIRQServiceRoutineHi lda #<.initNMI sta KERNALNMIServiceRoutineLo lda #>.initNMI sta KERNALNMIServiceRoutineHi ; Turn off various bits in the VIC2 and SID chips ; Screen, sprites and volume are disabled. lda #0 sta VIC2ScreenColour sta VIC2BorderColour sta VIC2ScreenControlV sta VIC2SpriteEnable ; Setup raster IRQ lda #<IrqTopOfScreen sta KERNALIRQServiceRoutineLo lda #>IrqTopOfScreen sta KERNALIRQServiceRoutineHi lda #1 sta VIC2InteruptControl lda #.theLine sta VIC2Raster lda #$1b sta VIC2ScreenControlV lda #2 sta VIC2BorderColour +MACROAckAllIRQs_A cli .mainLine ; Wait for the top IRQ to be triggered lda .topIRQDone beq .mainLine ; If fire is pressed then don't update the counter lda #%10000 bit CIA1KeyboardColumnJoystickA beq .mainLine lda #0 sta .topIRQDone ldx .xPosOffset inx cpx #40 bne .o1 ldx #0 .o1 stx .xPosOffset jmp .mainLine .topIRQDone !by 0 .xPosOffset !by 0 ; Remove all possibility that the timings will change due to previous code !align 255,0 IrqTopOfScreen ; Line 45 pha txa pha tya pha inc .topIRQDone lda #<.irq2 ldx #>.irq2 sta KERNALIRQServiceRoutineLo stx KERNALIRQServiceRoutineHi inc VIC2Raster +MACROAckRasterIRQ_A ; Begin the raster stabilisation code tsx cli ; These nops never really finish due to the raster IRQ triggering again nop nop nop nop nop nop nop nop nop nop nop nop nop nop .irq2 ; Line 46 txs ; Delay for a while ldx #8 .l1 dex bne .l1 bit $ea nop ; Final cycle wobble check. lda #.theLine+1 cmp VIC2Raster beq .start .start ; The raster is now stable ; Line 47 lda #$11 sta VIC2ScreenControlV ; Waste some time nop nop nop nop nop nop nop nop nop nop nop bit $ea ; Still in line 47 ; Calculate a variable offset to delay by branching over nops lda #39 sec sbc .xPosOffset ; divide by 2 to get the number of nops to skip lsr sta .sm1+1 ; Force branch always clv ; Line 48 ; Introduce a 1 cycle extra delay depending on the least significant bit of the x offset bcc .sm1 .sm1 bvc * ; The above branches somewhere into these nops depending on the x offset position nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop ; Show the raster position is stable and varies as a function of x offset ; If these border colour changes are removed then they need to be replaced with the same ; cycle count of nops inc VIC2BorderColour dec VIC2BorderColour ; Do the HSP by tweaking the VIC2ScreenControlV register at the correct time lda #$1b dec VIC2ScreenControlV inc VIC2ScreenControlV sta VIC2ScreenControlV ; Restart the IRQ chain lda #<IrqTopOfScreen ldx #>IrqTopOfScreen ldy #.theLine sta KERNALIRQServiceRoutineLo stx KERNALIRQServiceRoutineHi sty VIC2Raster +MACROAckRasterIRQ_A ; Exit the IRQ pla tay pla tax pla .initIRQ .initNMI rti
base/horizontal_screen_positioning_hsp.txt · Last modified: 2024-03-13 02:05 by martin_piper