Software Support Considerations

The MVME172 makes the following assumptions and supports a limited subset of RMW instructions. The MVME172 supports single-address RMW cycles caused by TAS and CAS instructions. Because it is not possible to tell if the MC68060 is executing a single- or multiple-address read-modify-write cycle, software should only execute single-address RMW instructions. Multiple-address RMW cycles caused by CAS or CAS2 instructions are not guaranteed indivisible and may cause illegal VMEbus cycles. Lock cycles caused by MMU table walks do not cause illegal VMEbus cycles, and they are not guaranteed indivisible.

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Illegal Access to IP Modules from External VMEbus Masters

When a device other than the local MVME172 is operating as VMEbus master, access by that device to the local IP modules is subject to restrictions.

Access to the IndustryPack memory space is supported in all cases. As a result of the difference in data width between the VMEbus and the IP modules (D32 versus D16), however, access to the IndustryPack I/O, ID, and Interrupt Acknowledge space is not supported for single IP modules. This applies to IndustryPacks a, b, c, and d.

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Motorola MVME172 manual Illegal Access to IP Modules from External VMEbus Masters