13 October 2020, 22:05 | #1 |
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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 $0001 nop nop or.l D0,D2 |
13 October 2020, 22:22 | #2 |
Lemon. / Core Design
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I don't think it's a vanilla 68000 instruction ?
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13 October 2020, 22:35 | #3 |
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It's a 68851 mmu instruction (psbc d1).
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13 October 2020, 22:36 | #4 |
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WinUAE disassembles it as Illegal Instruction.
Action Replay disassembles it as PSBC D1 Very odd - not seen that before. |
13 October 2020, 22:50 | #5 |
Defendit numerus
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Confirmed in qemu source:
{"psbc", 4, two(0xf040, 0x0001), two(0xffc0, 0xffff), "$s", m68851 }, 0xf040->d0, 0xf041->d1 and MC68851 manual (page 265) cc second instruction word BC B clear 000001 word Yes, PSBC D1 instruction. |
14 October 2020, 21:47 | #6 |
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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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14 October 2020, 22:25 | #7 |
Natteravn
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14 October 2020, 22:32 | #8 |
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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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14 October 2020, 22:54 | #9 |
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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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15 October 2020, 16:29 | #10 |
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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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15 October 2020, 17:20 | #11 |
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15 October 2020, 17:22 | #12 | |
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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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15 October 2020, 17:33 | #13 |
WinUAE developer
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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) |
15 October 2020, 17:49 | #14 | |
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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 October 2020, 20:01 | #15 | ||
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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 October 2020, 15:05 | #16 |
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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). |
16 October 2020, 18:58 | #17 |
Amigan
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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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16 October 2020, 19:00 | #18 |
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Repeat reply: I don't think they use any 68851-only features.
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16 October 2020, 19:13 | #19 | |
Natteravn
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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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16 October 2020, 22:18 | #20 | ||
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Quote:
Quote:
Last edited by DrBong; 16 October 2020 at 22:24. |
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