Path: utzoo!attcan!uunet!cs.utexas.edu!oakhill!shebanow From: shebanow@oakhill.UUCP (Mike Shebanow) Newsgroups: comp.arch Subject: Re: Instruction (dis)continuation Summary: Restart vs Continuation and Virtual machines are not related Message-ID: <2345@oakhill.UUCP> Date: 27 Aug 89 20:32:01 GMT References: <1989Aug24.215104.156@mentor.com> <231@ssp1.idca.tds.philips.nl> Reply-To: shebanow@oakhill.UUCP (Mike Shebanow) Organization: Motorola Inc., Austin, Texas Lines: 27 In article <231@ssp1.idca.tds.philips.nl> roelof@idca.tds.PHILIPS.nl (R. Vuurboom) writes: >I've noticed that motorola has moved from instruction continuation >(68010-30) to instruction restart (68040). So they no longer support >virtual machines. (Must be the processors got tired of puking their >insides all over the stack. :-) > >Quoting the 68030 manual: > >Instruction continuation is used to support virtual I/O devices in >memory-mapped input/output systems. Control and data registers for >the virtual are simulated in the memory map. An access to a virtual >register causes a fault and the function of the register is emulated >by software. You can still emulate virtual machines using instruction restart. All you have to do is simply interpret the instruction which faulted :-\ That is, when the machine takes the exception, the stack frame will point to the offending instruction. At that point, software can interpret this instruction and perform the intended operation. The only change is that software has to do all the work, not just part of it. Mike Shebanow ------------------------ Disclaimer: The opinions I have presented here are my own, not Motorola's.