
2-2
G2 PowerPC Core Reference Manual
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MOTOROLA
Register Set
for that purpose, such as the
mtspr
and
mfspr
instructions) or implicit as part of the
execution (or side effect) of an instruction. Some registers are accessed both explicitly and
implicitly.
Figure 2-1 describes both the registers in the G2 core and the additional registers of the
G2_LE core. All G2 core registers are present in the G2_LE core. Also note that the
implementation-specific registers for the G2 and G2_LE cores are shown in Figure 2-1.
The number to the right of the register name indicates the number that is used in the syntax
of the instruction operands to access the register (for example, the number used to access
the XER is SPR1).
For more information on the PowerPC register set, refer to Chapter 2, “Register Set,” in the
Programming Environments Manual
.
The G2 core user-level registers are described as follows:
User-level registers (UISA)—The user-level registers can be accessed by all
software with either user or supervisor privileges. The user-level register set
includes the following:
— General-purpose registers (GPRs). The GPR file consists of thirty-two 32-bit
GPRs designated as GPR0–GPR31. This register file serves as the data source or
destination for all integer instructions and provides data for generating
addresses.
— Floating-point registers (FPRs). The FPR file consists of thirty-two 64-bit FPRs
designated as FPR0–FPR31, which serves as the data source or destination for
all floating-point instructions. These registers can contain data objects of either
single- or double-precision floating-point format.
Before the
stfd
instruction is used to store the contents of an FPR to memory, the
FPR must have been initialized after reset (explicitly loaded with any value) by
using a floating-point load instruction.
— Condition register (CR). The CR consists of eight 4-bit fields, CR0–CR7, that
reflect the results of certain arithmetic operations and provides a mechanism for
testing and branching.
— Floating-point status and control register (FPSCR). The 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.
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.