Supervisor Stack Pointer (MC68060)

Note Software emulation of CAS2 and misaligned CAS instructions is performed by the MC68060 Software Package, which is included in all Motorola-supplied operating systems for the MVME177P. Contact your sales office for information about obtaining the MC68060 Software Package for use with other operating systems.

The single-board computers do not fully support all RMW operations in all possible cases. The modules make the following assumptions and support a limited subset of RMW instructions:

The single-board computers support single-address RMW cycles.

Multiple-address RMW cycles are not guaranteed indivisible and may cause illegal VMEbus cycles.

Lock cycles caused by MMU table walks on the VMEbus do not cause illegal VMEbus cycles but they are not guaranteed do be indivisible.

On M68000-based systems, aligned CAS and all TAS cycles are always single-address RMW operations, while misaligned CAS and CAS2 operations and operations in the MMU can be multiple-address RMW cycles. The VMEbus does not support multiple-address RMW cycles and there is no defined protocol for supporting multiple-address RMW cycles that start onboard and then access offboard resources. Because it is not possible to tell if the processor is executing a single- or multiple-address read-modify-write cycle, software should only execute single-address RMW instructions. For efficiency, all CAS instructions should be aligned.

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Supervisor Stack Pointer (MC68060)

On the MC68060, use of the supervisor stack pointer is reserved for system programming functions. All application software must be written to run in user mode. Such software will migrate to any M68000 platform without modification.

Programs written for platforms like the MC68040, which do use the supervisor stack pointer, must be recompiled before you can run them on a MC68060-based single-board computer such as the MVME177.

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Motorola MVME1X7P manual Supervisor Stack Pointer MC68060