are there any 68000 multi-cpu systems out there?

Jim wrote: The MC68000 didn't have a double bus fault problem. It had a *single* bus fault problem! On either a bus error or an address error exception, the information the processor puts in the exception stack frame is not sufficient to either resume or undo the faulted instruction. [*] These errors were considered fatal, and the typical "recovery" was to kill the process that faulted. Obviously this is not conducive to implementation of virtual memory. What some companies did, perhaps including Metheus, was to use two MC68000 processors. When a page fault occurs, rather than signalling a bus error to the running processor, the hardware "suspends" that processor (disconnects it from the bus, but leaves it waiting for the memory cycle to complete). The hardware enables the other processor, which runs the page fault hander. When the fault handler completes, the hardware switches back to the first processor, which can then complete the cycle. The MC68010 was introduced largely to fix this problem, though it had a few other enhancements as well. In the MC68010 (and MC68012, MC68020, MC68030, and CPU32), on a bus error or address error the processor pushes enough of its internal state onto the stack that an page fault handler can determine exactly what memory access had an error, fix the problem (e.g., by bringing in a page from disk and updating the page tables), and resume the faulted instruction from where it left off. The bus error stack frame was affectionately known as the "stack puke". On the MC68010, this occupied 29 16-bit words, although only 26 of them were written, and 3 were reserved. About 16 words of it were undocumented internal state that the software was not supposed to touch. On the M68K family processors, if a bus error occurred while the processor was already handling a bus error, that was a double bus fault and would cause a processor halt. This would normally only happen due to a software bug, such as a failure to allocate enough pages for the supervisor stack, and there was no means of recovery other than a hardware reset. In principle a multiple processor hack as described above could be used to allow recovery from this condition, but there wasn't really any reason to do so. Eric [*] If you write software such that only specific, known instructions can generate bus faults, you can recover from them. This technique is called probing, and is used in the Apple Lisa operating system.