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Flavioweb
Registered: Nov 2011
Posts: 463 |
[C128] Irq question ...
How can i make this code run on a C128 exactily at same addressess?
(I hope this isn't too much off-topic here...)
.C:3000 78 SEI
.C:3001 A9 7F LDA #$7F
.C:3003 8D 0D DC STA $DC0D
.C:3006 A9 00 LDA #$00
.C:3008 8D 14 03 STA $0314
.C:300b A9 40 LDA #$40
.C:300d 8D 15 03 STA $0315
.C:3010 A9 FF LDA #$FF
.C:3012 8D 12 D0 STA $D012
.C:3015 A9 01 LDA #$01
.C:3017 8D 1A D0 STA $D01A
.C:301a 4E 19 D0 LSR $D019
.C:301d 58 CLI
.C:301e 4C 1E 30 JMP $301E
.C:4000 EE 20 D0 INC $D020
.C:4003 EE 21 D0 INC $D021
.C:4006 AD 12 D0 LDA $D012
.C:4009 CD 12 D0 CMP $D012
.C:400c F0 FB BEQ $4009
.C:400e CE 20 D0 DEC $D020
.C:4011 CE 21 D0 DEC $D021
.C:4014 4E 19 D0 LSR $D019
.C:4017 4C 33 FF JMP $FF33 |
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Krill
Registered: Apr 2002
Posts: 2980 |
Not sure what your problem is, but the BASIC ROM on C-128 is at $4000, so you want to disable it in order to use the interrupt handler:lda #$02
sta $ff00 What's the background of your question? |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
The problem is here:
ff17 48 PHA - A:00 X:17 Y:00 SP:17 - I
ff18 8A TXA - A:00 X:17 Y:00 SP:16 - I
ff19 48 PHA - A:17 X:17 Y:00 SP:16 - I
ff1a 98 TYA - A:17 X:17 Y:00 SP:15 - I
ff1b 48 PHA - A:00 X:17 Y:00 SP:15 - IZ
ff1c AD 00 FF LDA $FF00 - A:00 X:17 Y:00 SP:14 - IZ
ff1f 48 PHA - A:00 X:17 Y:00 SP:14 - IZ
ff20 A9 00 LDA #$00 - A:00 X:17 Y:00 SP:13 - IZ
ff22 8D 00 FF STA $FF00 - A:00 X:17 Y:00 SP:13 - IZ
ff25 BA TSX - A:00 X:17 Y:00 SP:13 - IZ
ff26 BD 05 01 LDA $0105,X - A:00 X:13 Y:00 SP:13 - I
ff29 29 10 AND #$10 - A:20 X:13 Y:00 SP:13 - I
ff2b F0 03 BEQ $FF30 - A:00 X:13 Y:00 SP:13 - IZ
ff30 6C 14 03 JMP ($0314) - A:00 X:13 Y:00 SP:13 - IZ
at $FF20 kernal set $FF00 to $00 turning on BASIC again...
There is a way to avoid this but having kernal (not BASIC) rom active? |
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Krill
Registered: Apr 2002
Posts: 2980 |
Ah, i see. Then you either want to disable the KERNAL ROM as well and have your entirely own interrupt handler with the vector at $fffe, or you let the vector at $0314 point to a thunk residing anywhere below $4000, which would disable the BASIC ROM and then jump to the actual handler at $4000. |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
I need to have kernal on but basic off, using vector at $0314 to point the IRQ routine at $4000... |
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Krill
Registered: Apr 2002
Posts: 2980 |
Okay, XY problem solving time. What is your _actual_ problem you're trying to solve? |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
I'm experimenting using CC65 with a mix of C and assembly code.
An IRQ handler that setup one raster irq is called by C code.
Compiled C code starts with:
.C:1c0d A9 0E LDA #$0E
.C:1c0f 20 D2 FF JSR $FFD2
.C:1c12 AD 00 FF LDA $FF00
.C:1c15 48 PHA
.C:1c16 A9 0E LDA #$0E
.C:1c18 8D 00 FF STA $FF00
so ROMS are OFF.
Irq setup code starts at $4xxx and looks like:
.C:4011 A9 7F LDA #$7F
.C:4013 8D 0D DC STA $DC0D
.C:4016 78 SEI
.C:4017 A9 44 LDA #$44
.C:4019 8D 14 03 STA $0314
.C:401c A9 40 LDA #$40
.C:401e 8D 15 03 STA $0315
.C:4021 A9 64 LDA #$64
.C:4023 8D 18 03 STA $0318
.C:4026 A9 40 LDA #$40
.C:4028 8D 19 03 STA $0319
.C:402b A9 01 LDA #$01
.C:402d 8D 1A D0 STA $D01A
.C:4030 A9 1B LDA #$1B
.C:4032 8D 11 D0 STA $D011
.C:4035 A9 FC LDA #$FC
.C:4037 8D 12 D0 STA $D012
.C:403a AD 0D DC LDA $DC0D
.C:403d A9 0E LDA #$0E
.C:403f 8D 00 FF STA $FF00
.C:4042 58 CLI
.C:4043 60 RTS
which have a (now i know) useless $FF00 write at $403d.
After CLI at $4042, first time IRQ is triggered i have BASIC rom turned ON by kernal IRQ code... and all fucks up.
There is a way to keep BASIC OFF? |
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Krill
Registered: Apr 2002
Posts: 2980 |
But why must your interrupt handler start at $4000 and not, say, $3f80? And is that interrupt handler thunk/trampoline i mentioned not an option? |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
Because it look a really stupid thing to me...
I take it as last chance. Is a useless waste of cycles.
If i want to use ram under basic i need to set a code in the ram accessible by defalut, then set $FF00 and jmp to irq code.
I'm trying to understand if there is a way to "reconfigure" the bank activated by $00 in $FF00 to keep only kernal ON...
But is just my guess... i don't know if there is a way to do it... |
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Krill
Registered: Apr 2002
Posts: 2980 |
There isn't.
If the number of cycles is a problem for you, why not disable the ROM altogether and have your own interrupt handler called directly via $fffe/f? Would both consume a minimal amount of cycles and not have the BASIC ROM problem. |
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Krill
Registered: Apr 2002
Posts: 2980 |
Besides, having interrupt handlers below $4000 (or at $c000+) is a good idea because of the two RAM banks. You really want to enable a common area (configurable to up to 16K) and put your interrupt handlers there, otherwise having interrupt handlers in one bank and the code being interrupted in another could be a bit of a nuisance. |
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oziphantom
Registered: Oct 2014
Posts: 490 |
yeah its a flaw in the KERNAL sadly.. it should have been something like
ff1c AD 00 FF LDA $FF00 - A:00 X:17 Y:00 SP:14 - IZ
ff1f 48 PHA - A:00 X:17 Y:00 SP:14 - IZ
ff20 8D 00 FF STA $FF04 - A:00 X:17 Y:00 SP:13 - IZ
but then it has issues as well. Another flaw of this is it assumes the Stack is at $100 which isn't always true either.. and can lead to fun "why did the monitor just start" scratching head sessions - the lack of chis on x128 can really hurt sometimes.
I remember Bil Herd saying that post release he ask Fred why he didn't use the MMU, and his response was "Because there are no Kernal only registers", to which Bil responded "Why didn't you tell me.."
The handy thing with the Pre Configs is they don't trash a register, so you could put your IRQ at $3FFD
0:3FFD sta FF02 <- disable BASIC LO, HI,EDITOR,MONITOR
0:4000 pha
0:4001 tax
.....
You need to set up the PreConfigs to be what you want first, but it only adds 4 clocks |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
WTF they choosed to force ROMS ON anyway!?!
If i disable the roms and computer crashes ... are just my businness!
If i want to setup a IRQ under ROMS the only way is to disable kernal... or put a "trampoline" in a ram area...
If i need kernal in other parts of my code, outside the irq, the only solution is to have a trampoline somewhere...
/o\ |
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Oswald
Registered: Apr 2002
Posts: 5094 |
well trampoline it, you only waste some bytes in ram, you can even enter the rom irq faster by bypassing some of it. |
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oziphantom
Registered: Oct 2014
Posts: 490 |
If you know its not going to be used, you can set up the JMPFAR routine $02/$03/$04 bank lo hi and just point the IRQ vector to x:02e3 |
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Krill
Registered: Apr 2002
Posts: 2980 |
Just have a two-fold approach.
- KERNAL disabled would go to your actual interrupt handler directly via $fffe/f.
- KERNAL enabled would go to the ROM interrupt handler, then to the trampoline via $0314/5, which would then go to the actual interrupt handler.
This way, you're only using the cycles you really need to use while allowing both KERNAL on and off. |
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oziphantom
Registered: Oct 2014
Posts: 490 |
But yes, welcome to the 128, it has ROM EVERYWHERE, however you can switch out the CHARGEN EVERYWHERE as well which is nice. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: Just have a two-fold approach.
- KERNAL disabled would go to your actual interrupt handler directly via $fffe/f.
- KERNAL enabled would go to the ROM interrupt handler, then to the trampoline via $0314/5, which would then go to the actual interrupt handler.
This way, you're only using the cycles you really need to use while allowing both KERNAL on and off.
This is exactly what I do in EotB and my oen handler mimics the kernel so that timing is the same (not c128 related) |
