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Forums > C64 Coding > Loading and saving to disk using kernel
2018-06-13 18:59
JackAsser

Registered: Jun 2002
Posts: 1458
Loading and saving to disk using kernel

Assume: Machine booted from cart. Cart ROM at $8000-$bfff. IO at $Dxxx and KERNAL at $e000-$ffff

What calls do I have to do to use KERNEL load/save?
What RAM and ZP will be trashed by this?
How will it affect my IRQs? (I have CIA1 and raster IRQs running via $0314/15)
 
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2018-06-14 21:05
JackAsser

Registered: Jun 2002
Posts: 1458
Quote: @JackAsser: Don't know if its of any value for you but if you use $ee13 you can jump to $ee20 instead and use

LDA #$00
STA $A5
JSR $EE85
JSR $EEA9
BPL *-3
SEI
jsr $ee20

with moving the SEI below the BPL the routine just rips ~30 rasterlines while loading. One might call it "pretty cheap irq loader" :-D

Org (KERNAL):

.,EE13 78 SEI
.,EE14 A9 00 LDA #$00
.,EE16 85 A5 STA $A5
.,EE18 20 85 EE JSR $EE85
.,EE1B 20 A9 EE JSR $EEA9
.,EE1E 10 FB BPL $EE1B

PS: AFAIR the source of this "trick" was some issue of "64er"


Thanks! I’ll keep it simple and just clear the area where the IRQ was needed though. I have a multiplexed sprite overlay which will get distorted even with the trick u mentioned. So let’s forget about IRQ and focus on Kernel memory footprint.
2018-06-14 22:27
Flavioweb

Registered: Nov 2011
Posts: 362
Quoting JackAsser
I have a multiplexed sprite overlay which will get distorted even with the trick u mentioned. So let’s forget about IRQ and focus on Kernel memory footprint.

Mmmm... if you have 8 sprites in a row on the screen, Iec transfers goes out of sync, even without any Irq code running...
Is safe turn off all sprites during save/load...
2018-06-15 06:13
Grue

Registered: Dec 2001
Posts: 100
While these tricks are nice and clever keep in mind that it will break compability with alternative kernals.


Quoting Danzig
@JackAsser: Don't know if its of any value for you but if you use $ee13 you can jump to $ee20 instead and use

LDA #$00
STA $A5
JSR $EE85
JSR $EEA9
BPL *-3
SEI
jsr $ee20

with moving the SEI below the BPL the routine just rips ~30 rasterlines while loading. One might call it "pretty cheap irq loader" :-D

Org (KERNAL):

.,EE13 78 SEI
.,EE14 A9 00 LDA #$00
.,EE16 85 A5 STA $A5
.,EE18 20 85 EE JSR $EE85
.,EE1B 20 A9 EE JSR $EEA9
.,EE1E 10 FB BPL $EE1B

PS: AFAIR the source of this "trick" was some issue of "64er"
2018-06-15 07:23
JackAsser

Registered: Jun 2002
Posts: 1458
Yeah, I keep it simple and blank the screen. Speaking of alternative Kernels... what about their memory footprint while loading/saving?
2018-06-15 08:49
Flavioweb

Registered: Nov 2011
Posts: 362
To avoid problems with the pletora of alternative fl, you can just backup/reset/restore the vectors.
But should be interesting to investigate this...
2018-06-15 14:48
JackAsser

Registered: Jun 2002
Posts: 1458
Quote: To avoid problems with the pletora of alternative fl, you can just backup/reset/restore the vectors.
But should be interesting to investigate this...


The vectors are one thing, but I would imagine an alternative kernel to perhaps reserve a 256 byte sector buffer for speed etc no? Or are they all "compatible" to each other? Or is it simply assumed that ZP and $200-$3ff is a no-go for own code when it comes to kernel compatibility?
2018-06-15 15:29
cadaver

Registered: Feb 2002
Posts: 1068
I go by the assumption that any alternative kernal will not use at least more memory or more ZP locations, may come to yet bite my ass :)

Outside ZP starting your own memory use from $0334 should be OK, no need to avoid $0334-$03ff range unless you use tape IO.
2018-06-15 18:26
ChristopherJam

Registered: Aug 2004
Posts: 843
Quoting Oswald
kernAl

And Betty when you call me you can calllll, meeeee, Al :)
2018-06-19 11:54
Martin Piper

Registered: Nov 2007
Posts: 393
Code used for Berzerk Redux. I used the disk drive for hiscore storage with an optional custom load/save: https://github.com/martinpiper/C64Public/blob/master/BerzerkRed..

Citadel2 cartridge code, works with kernal replacement and CBM80 boot carts (EF and GMod2). Also tests cart banking: https://github.com/martinpiper/C64Public/blob/master/Citadel2/C..
2018-06-19 11:55
JackAsser

Registered: Jun 2002
Posts: 1458
Quote: Code used for Berzerk Redux. I used the disk drive for hiscore storage with an optional custom load/save: https://github.com/martinpiper/C64Public/blob/master/BerzerkRed..

Citadel2 cartridge code, works with kernal replacement and CBM80 boot carts (EF and GMod2). Also tests cart banking: https://github.com/martinpiper/C64Public/blob/master/Citadel2/C..


Awesome Martin! Thanks!
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