
MOTOROLA
Chapter 1. Overview
1-5
Overview
— Support for one-level address pipelining and out-of-order bus transactions on the
60x interface
— True little-endian mode (for G2_LE only) for compatibility with other true
little-endian devices.
— Critical interrupt exception (for G2_LE only) is added
— Hardware support for misaligned little-endian accesses
Integrated power management
— Internal processor/bus clock multiplier ratios
— Three power-saving modes: doze, nap, and sleep
— Automatic dynamic power reduction when internal functional units are idle
In-system testability and debugging features through JTAG boundary-scan
capability
Features specific to the G2 core not present on the original MPC603e (PID6-603e)
processors follow:
Enhancements to the register set
— The G2 core has two more additional HID0 bits then the original MPC603e:
– The address bus enable (ABE) bit, HID0[28], gives the G2 core the ability to
broadcast
dcbf
,
dcbi
, and
dcbst
onto the 60x bus.
– The instruction fetch enable M (IFEM) bit, HID0[24], allows the G2 core to
reflect the value of the M bit during instruction translation onto the 60x bus.
— The G2 core has one more additional HID2 register than the original MPC603e
that enables the true little-endian mode, the new additional BAT registers, and
cache way-locking for the G2 core.
Enhancements to cache implementation
— The instruction cache is blocked only until the critical load completes (hit under
reloads allowed)
— The critical-double-word is simultaneously written to the cache and forwarded
to the requesting unit, thus minimizing stalls due to load delays.
— The HID2 register enables instruction and data cache way-locking.
— Provides for an optional data cache operation broadcast feature (enabled by
HID0[ABE]) that allows for correct system management using an external
copy-back L2 cache.
— All of the cache control instructions (
icbi
,
dcbi
,
dcbf
, and
dcbst
, excluding
dcbz
) require that HID0[ABE] be enabled in order to execute.
Exceptions
— The G2 core offers hardware support for misaligned little-endian accesses.
Little-endian load/store accesses that are not on a word boundary, with the
F
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n
.