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Ben
Account closed
Registered: Feb 2003
Posts: 163 |
Free cycles in raster line..
Is there some sort of stable, line dense raster leaving some cycles per line free which can then be filled with instructions executed outside the IRQ?
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WVL
Registered: Mar 2002
Posts: 886 |
you can make an nmi that you trigger each 63 cycles maybe.. then you have to take care of turning the nmi's on/off by yourself though (or you have to make 200 separate nmi's ;)
for some examples, look at some nmi sample players. |
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yago
Registered: May 2002
Posts: 332 |
Some hints when using nmis for rasters:
nmis should be turned on with stable irq
only use accumulator inside nmi-routine
so that only
pha
;some routine
pla
rti
is neccesary.
To turn the nmis off, a normal raster-irq is sufficient.
And to spare some additional cycles, ROM should be turned off.
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WVL
Registered: Mar 2002
Posts: 886 |
Quote: Some hints when using nmis for rasters:
nmis should be turned on with stable irq
only use accumulator inside nmi-routine
so that only
pha
;some routine
pla
rti
is neccesary.
To turn the nmis off, a normal raster-irq is sufficient.
And to spare some additional cycles, ROM should be turned off.
and yago is wasting cycles immediately! ;)
better not to use pha/pla, that costs you 7 cycles! rather put the code in the 0page, and do
sta loada
;some routine
loada=*+1
lda #$00
rti
which is only 5 cycles for saving & restoring the accumulator.. 2 cycles profit of the max 63 available. You can buy me a beer at PS.
cycles, my precioussssss |
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Ben
Account closed
Registered: Feb 2003
Posts: 163 |
Quote: and yago is wasting cycles immediately! ;)
better not to use pha/pla, that costs you 7 cycles! rather put the code in the 0page, and do
sta loada
;some routine
loada=*+1
lda #$00
rti
which is only 5 cycles for saving & restoring the accumulator.. 2 cycles profit of the max 63 available. You can buy me a beer at PS.
cycles, my precioussssss
Since beer is for free at PS, I will just go and fetch you one then :) |
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tlr
Registered: Sep 2003
Posts: 1724 |
Quote: you can make an nmi that you trigger each 63 cycles maybe.. then you have to take care of turning the nmi's on/off by yourself though (or you have to make 200 separate nmi's ;)
for some examples, look at some nmi sample players.
We did this in 6566+. There is an interrupt on each raster line, even though we decided on colors that doesn't change at every line.
It won't be more stable than within roughly 7 cycles depending on what code you run in the background, but it will always stay around the desired point.
If you want it on the exact same cycle every time you will have to waste cycles to take up the jitter every interrupt. |
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yago
Registered: May 2002
Posts: 332 |
Marko Makela described this Technique in C=Hacking #10.
http://www.ffd2.com/fridge/chacking/
@WVL: OK, I'll give you a Karlsquell.
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Ben
Account closed
Registered: Feb 2003
Posts: 163 |
Quote: We did this in 6566+. There is an interrupt on each raster line, even though we decided on colors that doesn't change at every line.
It won't be more stable than within roughly 7 cycles depending on what code you run in the background, but it will always stay around the desired point.
If you want it on the exact same cycle every time you will have to waste cycles to take up the jitter every interrupt.
I see you are using:
thing pha
lda $dd0d
inc foo+1
foo lda $0800
sta $d021
sta $d020
pla
rti
You however seem to destroy the initialization of the interrupts on purpose :)
I reckon you do something like
lda #<thing
ldx #>thing
sta $0316
stx $0317
to launch the NMI
7 cycles jitter is quite a blow.. is there any mechanism allowing one to stabilize the raster in any fashion, e.g. to appropriate the routine for open sideborder? |
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Ben
Account closed
Registered: Feb 2003
Posts: 163 |
Quote: Marko Makela described this Technique in C=Hacking #10.
http://www.ffd2.com/fridge/chacking/
@WVL: OK, I'll give you a Karlsquell.
Nice magazine :) Thanks for the link! |
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tlr
Registered: Sep 2003
Posts: 1724 |
Quote: I see you are using:
thing pha
lda $dd0d
inc foo+1
foo lda $0800
sta $d021
sta $d020
pla
rti
You however seem to destroy the initialization of the interrupts on purpose :)
I reckon you do something like
lda #<thing
ldx #>thing
sta $0316
stx $0317
to launch the NMI
7 cycles jitter is quite a blow.. is there any mechanism allowing one to stabilize the raster in any fashion, e.g. to appropriate the routine for open sideborder?
We thought we were the first doing full screen rasters with sprites over them + music running, so we wanted to set the competition back a bit. ;) (also I was 14 years old)
The over writing is done when starting the code, but ironically I forgot the packed version at $8000. :P
Note that Rob Hubbards Zoolook was manually relocated to
$090d to get a contiguous block just for show off. :)
BTW: I still haven't found anyone doing this before us, does anyone here know an earlier example of this technique?
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tlr
Registered: Sep 2003
Posts: 1724 |
Quote: I see you are using:
thing pha
lda $dd0d
inc foo+1
foo lda $0800
sta $d021
sta $d020
pla
rti
You however seem to destroy the initialization of the interrupts on purpose :)
I reckon you do something like
lda #<thing
ldx #>thing
sta $0316
stx $0317
to launch the NMI
7 cycles jitter is quite a blow.. is there any mechanism allowing one to stabilize the raster in any fashion, e.g. to appropriate the routine for open sideborder?
That should be $0318/$0319, but it would be much better to use $fffa/$fffb.
Also the 7 cycles (or is it 6?) depend on the fact that the longest 6510 instruction is 7 cycles (eg "inc abs,x"). If you restrict which instructions you run, you will get less jitter. If you want it really stable you'll have to use the timer value to compensate, which won't leave many cycles at all for stuff to run in the background.
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