wall@fortune.UUCP (Jim Wall) (08/13/86)
Is Motorola still on the net? Probably, if I'm still at Fortune, they're still on the net, somethings never change. When you do a read-modify-write instruction on a systen that uses a PMMU or the infamous MMB from Motorola the odds are taht a table walk will be required, unfortunately, the bus request from the PMMU will be ignored by the 68020 because the RMC is an indivisable cycle and so bus requests are ignored, the upshot is that the system hangs. This is ture for the MMB, nothing I see will fix this for the PMMU chip in its final form. Any one care to comment? I'm assuming this to be the case, and since I have no time to pursue it, software will work around it. THis is partially for peoples edification, and partially to see if I'm understanding the situation correctly. -Jim Wall Fortune Systems Corp.
cruess@oakhill.UUCP (Michael Cruess) (08/16/86)
Old versions of the MMB (manufactured more than about 2 years ago) would lock up. Newer versions of the MMB do not. The PMMU (68851) does not and never has. Please see *MC68851 Paged Memory Management Unit User's Manual* Section 6.3.1.7 READ-MODIFY-WRITE (RMW) CYCLE. Michael Cruess oakhill!cruess Motorola, Inc. Microprocessor Products Group