MOTOROLA
Chapter 2. PowerPC Processor Core
2-11
Part I. Overview
Although the MPC8260 does not support ßoating-point arithmetic instructions, the FPRs
are provided to support ßoating-point load and store instructions, which can be executed by
the LSU. For these instructions to execute, the FPRs must be enabled (MSR[FP] = 1);
otherwise, a ßoating-point unavailable exception is taken. It is recommended that the FPRs
be enabled only when there is a need to access the FPRs, for example, to handle ßash
memory updates. Otherwise, the processor should run in default mode, with FPRs disabled
(MSR[FP] = 0).
2.3.1.2 MPC8260-SpeciÞc Registers
The set of registers speciÞc to the MPC603e are also shown in Figure 2-2. Most of these
are described in the
MPC603e UserÕs Manual
and are implemented in the MPC8260 as
follows:
¥
MMU software table search registers: DMISS, DCMP, HASH1, HASH2, IMISS,
ICMP, and RPA. These registers facilitate the software required to search the page
tables in memory.
¥
IABR. This register facilitates the setting of instruction breakpoints.
The hardware implementation-dependent registers (HIDx) are implemented differently in
the MPC8260, and they are described in the following subsections.
2.3.1.2.1 Hardware Implementation-Dependent Register 0 (HID0)
The processor coreÕs implementation of HID0 differs from the
MPC603e UserÕs Manual
as
follows:
¥
Bit 5, HID0[EICE], has been removed. There is no support for pipeline tracking.
¥
Bit 24, HID0[IFEM], instruction fetch enable M, has been added.
¥
Bit 28, HID0[ABE], address broadcast enable, has been added.
Figure 2-3 shows the MPC8260 implementation of HID0.
Figure 2-3. Hardware Implementation Register 0 (HID0)
0
1
2
3
4
6
7
8
9 10 11 12
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
EBD
EBA
PAR
NAP
DPM NHR ICE DCE
DCFI
EMCP
DOZE
SLEEP
ILOCK
DLOCK
ICFI
FBIOB
NOOPTI
Ñ
Ñ
Ñ
IFEM
Ñ
Ñ
Ñ
ABE
Содержание MPC8260 PowerQUICC II
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