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#1 |
Registered User
Join Date: Mar 2018
Location: Hastings, New Zealand
Posts: 2,735
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What instruction is this? $F041 $0001
Devpac 3 and Barfly debuggers both refuse to disassemble the instruction shown in hex below (partial disassembly of ProAsm V1.92). Does anyone know what it is?
Code runs in supervisor mode and appears to be trying to determine the processor type or features. Code:
cmp.w #$0004,D2 beq.s w001570 . . w001570: dc.w $f041 <--- unknown instruction dc.w $0001 nop nop or.l D0,D2 |
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#2 |
Lemon. / Core Design
Join Date: Mar 2016
Location: Tier 5
Posts: 1,213
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I don't think it's a vanilla 68000 instruction ?
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#3 |
Registered User
Join Date: Jun 2008
Location: somewhere else
Posts: 524
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It's a 68851 mmu instruction (psbc d1).
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#4 |
Registered User
Join Date: Oct 2017
Location: Sunderland, England
Posts: 2,702
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WinUAE disassembles it as Illegal Instruction.
Action Replay disassembles it as PSBC D1 Very odd - not seen that before. |
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#5 |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 54
Posts: 4,491
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Confirmed in qemu source:
{"psbc", 4, two(0xf040, 0x0001), two(0xffc0, 0xffff), "$s", m68851 }, 0xf040->d0, 0xf041->d1 and MC68851 manual (page 265) cc second instruction word BC B clear 000001 word Yes, PSBC D1 instruction. |
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#6 |
This cat is no more
Join Date: Dec 2004
Location: FRANCE
Age: 52
Posts: 8,370
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Damn this is a rare chip I had never heard of before. Were there Amigas with 68020 and MC 68851 as MMU? I doubt WinUAE supports this either.
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#7 |
Natteravn
Join Date: Nov 2009
Location: Herford / Germany
Posts: 2,545
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#8 |
Registered User
Join Date: Sep 2017
Location: Kansas, USA
Posts: 329
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The A2620 could use the 68851, but I'm not sure if it was equipped as standard or optional.
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#9 |
This cat is no more
Join Date: Dec 2004
Location: FRANCE
Age: 52
Posts: 8,370
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I'm sure Toni will be delighted to support that chip in WinUAE, and Wepl will be thrilled to support that chip in Whdload
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#10 |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,573
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I don't think there are any Amiga programs that require 68851 or use 68851 features. First requirement for emulation some hardware: it needs software!
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#11 |
Registered User
Join Date: May 2013
Location: Grimstad / Norway
Posts: 853
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#12 | |
Registered User
Join Date: Jan 2008
Location: Warsaw/Poland
Age: 56
Posts: 2,046
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Quote:
http://www.sinz.org/Michael.Sinz/Enforcer/index.html OpenBSD? https://www.openbsd.org/amiga.html |
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#13 |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,573
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Do they actually use 68851-only features?
If program also supports 68030, modifying it to work with 68020+68851 does not require use of any 68851-only features. (68030 MMU is more or less integrated 68851 with lots of weird features dropped) |
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#14 | |
Registered User
Join Date: Jan 2008
Location: Warsaw/Poland
Age: 56
Posts: 2,046
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Quote:
* 68020 NOTES * The 68020 does not have a built-in MMU but has a co-processor * feature that lets an external MMU be connected. Enforcer MMU code * is designed for use with 68851 MMU. This is the some-what 68030 * compatible MMU by Motorola. Enforcer uses the same code for both * the 68030 and the 68020/68851. For this reason, 68020/68851 users * should see the 68030 NOTES section. |
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#15 | ||
HOL / AMR Team Member
Join Date: Dec 2001
Location: Australia
Posts: 2,632
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Quote:
Quote:
Last edited by DrBong; 15 October 2020 at 20:51. Reason: Added more links! |
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#16 |
Registered User
Join Date: Aug 2014
Location: Zagreb / Croatia
Posts: 302
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AMIX (Amiga UNIX) uses 68020+68851 or 68030 with MMU. Also WHDLoad can use MMU partially. (You know that there was 68451 MMU for 68000/010, but it was rarely used.)
There are 2 cpScc (cp = coprocessor) instructions: PScc (68851) and FScc (FPU; native on 68881, 68882 and 68040; software emulated on 68060 - in 68060.library on Amiga). |
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#17 |
Amigan
![]() Join Date: Feb 2012
Location: London
Posts: 1,317
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As NetBSD & AMIX are here I might we can add Linux/68k which Geert Uytterhoeven still seems to be supporting to this day.
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#18 |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,573
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Repeat reply: I don't think they use any 68851-only features.
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#19 | |
Natteravn
Join Date: Nov 2009
Location: Herford / Germany
Posts: 2,545
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Toni is probably right. The 851-specific features are rarely used. And I can confirm for NetBSD that 68851 and 68030 systems are treated the same.
Quote:
![]() (It can assemble 68851 mnemonics as many other assemblers do.) |
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#20 | ||
HOL / AMR Team Member
Join Date: Dec 2001
Location: Australia
Posts: 2,632
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Quote:
Quote:
![]() Last edited by DrBong; 16 October 2020 at 22:24. |
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