
MOTOROLA
Chapter 1. Overview
1-19
Implementation-Specific Information
1.3.1.3
Condition Register (CR)
The CR is a 32-bit user-level register that provides a mechanism for testing and branching.
It consists of eight 4-bit fields that reflect the results of certain operations, such as move,
integer and floating-point comparisons, arithmetic, and logical operations.
1.3.1.4
Floating-Point Status and Control Register (FPSCR)
The user-level FPSCR contains all floating-point exception signal bits, exception summary
bits, exception enable bits, and rounding control bits needed for compliance with the IEEE
754 standard.
1.3.1.5
Machine State Register (MSR)
The MSR is a supervisor-level register that defines the state of the core. The contents of this
register are saved when an exception is taken and restored when the exception handling
completes. A critical interrupt exception is taken only in the G2_LE core when the
core_cint signal is asserted and MSR[CE] is set. The G2 core implements the MSR as a
32-bit register.
1.3.1.6
Segment Registers (SRs)
For memory management, 32-bit processors implement sixteen 32-bit SRs. To speed
access, the core implements the SRs as two arrays; a main array (for data memory accesses)
and a shadow array (for instruction memory accesses). Loading a segment entry with the
Move to Segment Register
(
mtsr
)
instruction loads both arrays.
1.3.1.7
Special-Purpose Registers (SPRs)
The OEA defines numerous SPRs that serve a variety of functions, such as providing
controls, indicating status, configuring the core, and performing special operations. During
normal execution, a program can access the registers, as shown in Figure 1-2, depending
on the program’s access privilege (supervisor or user, determined by the privilege-level bit,
MSR[PR]). Note that GPRs and FPRs are accessed through operands that are part of the
instructions. Access to registers can be explicit (that is, through the use of specific
instructions for that purpose such as Move to Special-Purpose Register (
mtspr
) and Move
from Special-Purpose Register (
mfspr
) instructions) or implicit, as the part of the execution
of an instruction. Some registers are accessed both explicitly and implicitly.
The G2_LE core has 29 new/additional supervisor-level SPRs, which are shown in
Figure 1-2. Two critical interrupt SPRs (CSRR0 and CSRR1), four additional SPRGs
(SPRG4–SPRG7), four pairs of instruction BATs (IBAT4–IBAT7) and four pairs of data
BATs (DBAT4–DBAT7), one system version register (SVR), one system memory base
address (MBAR), one instruction address breakpoint control (IBCR) and one data address
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