
MOTOROLA
Chapter 2. Programming Model
2-7
– Decrementer (DEC). The DEC register is a 32-bit decrementing counter that
provides a mechanism for causing a decrementer exception after a
programmable delay. The DEC is decremented once every four bus clock
cycles.
– External access register (EAR). The EAR is a 32-bit register used in
conjunction with the
eciwx
and
ecowx
instructions. While the PowerPC
architecture specifies that the low-order six bits of the EAR (bits 26–31) are
used to select a device, the 603e only implements the low-order 4 bits (bits
28–31). Note that the EAR register and the
eciwx
and
ecowx
instructions are
optional in the PowerPC architecture and may not be supported in all
PowerPC processors that implement the OEA.
2.1.2 Implementation-Specific Registers
The 603e includes several implementation-specific SPRs that are not defined by the
PowerPC architecture. They are the DMISS, IMISS, DCMP, ICMP, HASH1, HASH2,
RPA, HID0, HID1, and IABR registers. These registers can be accessed by supervisor-level
instructions only. Any attempt to access these SPRs with user-level instructions results in a
supervisor-level exception. The SPR numbers for these registers are shown in Figure 2-1.
The DMISS, IMISS, DCMP, ICMP, HASH1, HASH2, and RPA registers are used for
software table search operations and should only be accessed when address translation is
disabled (that is, MSR[IR] = 0 and MSR[DR] = 0). For a complete discussion of software
table search operations, refer to Section 5.5.2, “Implementation-Specific Table Search
Operation.”
2.1.2.1 Hardware Implementation Registers (HID0 and HID1)
The HID0 and HID1 registers, shown in Figure 2-2 and Figure 2-3 respectively, define
enable bits for various 603e-specific features.
Figure 2-2. Hardware Implementation Register 0 (HID0)
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22
26 27 28
30 31
Reserved
EBD
EBA
PAR
NAP
DPM
NHR ICE DCE
DCFI
EMCP
SBCLK
EICE
ECLK
DOZE
SLEEP
RISEG
ILOCK
DLOCK
ICFI
FBIOB
NOOPTI
0 0 0 0 0
0 0 0
0 0
0