Motorola MVME1X7P User Manual
Supervisor Stack Pointer (MC68060)
http://www.motorola.com/computer/literature
1-53
1
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.
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:
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.
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.
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.
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.
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.
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.
supervisor stack pointer, must be recompiled before you can run them on
a MC68060-based single-board computer such as the MVME177.