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March 2002 Release
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Virtex-II Pro™ Platform FPGA Documentation
Appendix E:
PowerPC
®
6xx/7xx Compatibility
R
•
The programmable-interval timer (PIT) interrupt. This interrupt is triggered by a
time-out on the PIT registers. Its function replaces that of the decrementer interrupt in
the PowerPC 6xx/7xx family.
•
The fixed-interval timer (FIT) interrupt. This interrupt is triggered by a pre-
determined bit transition in the time base. This feature is not supported by the
PowerPC 6xx/7xx family.
•
The watchdog timer (WDT) interrupt. This critical interrupt is triggered by a pre-
determined bit transition in the time base. This feature is not supported by the
PowerPC 6xx/7xx family.
•
The timer-control register (TCR). This register controls the PowerPC 40x timer
resources. It is not supported by the PowerPC 6xx/7xx family.
•
The timer-status register (TSR). This register is used by the PowerPC 40x timer
resources to report status. It is not supported by the PowerPC 6xx/7xx family.
Other Differences
Instructions
PowerPC 40x processors can support implementation-specific instructions that are not
supported in PowerPC 6xx/7xx processors. For example, the multiply-accumulate (MAC)
instructions are not supported by PowerPC 6xx/7xx processors. Refer to
, for a list of implementation dependent PPC405 instructions. This table also
shows which PPC405 instructions are not supported by the PowerPC architecture.
Endian Support
The default memory-access order for all PowerPC processors is big-endian. The PowerPC
embedded-environment architecture defines a true little-endian memory-access capability
that is implemented using the endian storage attribute (E). The PPC405 supports this
capability. The PowerPC architecture supports a little-endian mode that is implemented by
PowerPC 6xx/7xx processors. This mode is not supported by the PPC405.
Debug Resources
Debug resources are implementation dependent. In general, all PowerPC 40x processors
support debug events on both instruction addresses and data addresses. Debug events are
controlled using the DBCR0 and DBCR1 registers. Debug status is reported by the DBSR
register. PowerPC 6xx/7xx processors support debug resources to varying degrees, but the
capabilities are often less comprehensive than those supported by PowerPC 40x
processors.
Power Management
The PowerPC 40x family implements power management using the MSR[WE] bit. Setting
this bit places the processor in the wait state. Power management is disabled when an
interrupt occurs.
The PowerPC 6xx/7xx family similarly implements power management using the
MSR[POW] bit. PowerPC 7xx processors support four different power states, programmed
using the HID0 register. Power management is disabled when an interrupt occurs.
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