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18 December 2019, 22:08
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#1 |
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Registered User
Join Date: Sep 2019
Location: Essen/Germany
Age: 55
Posts: 463
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movec on 68000
I'm converting ministartup from here: http://stingray.untergrund.net/MiniStartup.s and stumbled over this part:
Code:
.GetVBR move.l a5,-(a7) moveq #0,d0 ; default at $0 move.l $4.w,a6 btst #0,296+1(a6) ; 68010+? beq.b .is68k ; nope. lea .getit(pc),a5 jsr -30(a6) ; SuperVisor() .is68k move.l (a7)+,a5 rts .getit movec vbr,d0 rte ; back to user state code It executes the "movec" privileged instruction which is AFAIK an 68010+ instruction, right? So I get an error from vasm because I'm targetting 68000: instruction not supported on selected architecture And I wonder how to work around this, as I'm not sure what exactly it does. |
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18 December 2019, 22:24
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#2 |
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Going nowhere
Join Date: Oct 2001
Location: United Kingdom
Age: 50
Posts: 8,994
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Change the line MOVEC VBR,d0 to this:
dc.l $4E7A0801 VBR = Vector Base Register. On a 68000 the VBR cannot be moved, so the base address is $0. The Vector Base is the area of memory where the vectors are stored, so thats BUS ERROR etc and of course the interrupts. On 68010+ the Vector Base can be repositioned, and all those interrupts will also be moved. |
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18 December 2019, 22:40
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#3 |
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Registered User
Join Date: Sep 2019
Location: Essen/Germany
Age: 55
Posts: 463
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Thanks. I enabled 68010 instruction set. I was trying to find the encoding for the instruction.
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19 December 2019, 13:28
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#4 |
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Lemon. / Core Design
Join Date: Mar 2016
Location: Tier 5
Posts: 1,212
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this should do it:
mc68020 movec vbr,d0 mc68000 |
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19 December 2019, 13:32
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#5 |
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Registered User
Join Date: Sep 2019
Location: Essen/Germany
Age: 55
Posts: 463
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Thanks! I was looking on how to enable an architecture for only some instructions, but I haven't found this in the docs. This is much better, as I want to target 68000 and I wouldn't like to slip in other instructions by accident, as it would be possible at the moment.
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19 December 2019, 13:40
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#6 | |
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Going nowhere
Join Date: Oct 2001
Location: United Kingdom
Age: 50
Posts: 8,994
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Quote:
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19 December 2019, 14:23
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#7 |
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Registered User
Join Date: Sep 2019
Location: Essen/Germany
Age: 55
Posts: 463
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Yes, But it should be there, in case it is executed on a different machine, right? So the code wouldn't work, if the program would be started on some A1200 or so.
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19 December 2019, 15:08
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#8 |
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Lemon. / Core Design
Join Date: Mar 2016
Location: Tier 5
Posts: 1,212
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ministartup works perfectly well on all Amigas / processors / configs
On 68000, the movec part is never called, so it's just in effect some bytes in memory |
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19 December 2019, 15:44
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#9 |
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Registered User
Join Date: Sep 2019
Location: Essen/Germany
Age: 55
Posts: 463
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Yes, thats why I left it in.
I could have removed that part, but then it wouldn't work properly on other Amigas.
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