Register Model
e200z3 Power Architecture Core Reference Manual, Rev. 2
2-4
Freescale Semiconductor
Figure 2-1. e200z3 Programmer’s Model
2.1
PowerPC Book E Registers
The e200z3 supports most of the registers defined by Book E architecture. Notable exceptions are the
floating-point registers FPR0–FPR31 and the FPSCR. The e200z3 does not support the Book E
floating-point architecture in hardware. The GPRs are extended to 64 bits. The Book E registers in the
e200z3 are as follows:
•
User-level registers, which are accessible to all software with either user or supervisor privileges:
— General-purpose registers (GPRs). Thirty-two 64-bit GPRs (GPR0–GPR31) serve as data
source or destination registers for integer instructions and provide data to generate addresses.
PowerPC Book E instructions affect only the lower 32 bits of the GPRs. SPE APU instructions
operate on the entire 64-bit register.
— Condition register (CR). Eight 4-bit fields, CR0–CR7, reflect results of certain arithmetic
operations and provide a mechanism for testing and branching.
The remaining user-level registers are SPRs. In the PowerPC architecture, the mtspr and mfspr
instructions are for accessing SPRs.
— Integer exception register (XER). Indicates overflow and carries for integer operations.
— Link register (LR). Provides the branch target address for the branch conditional to link register
(bclr, bclrl) instructions and holds the address of the instruction that follows a branch and link
instruction, typically for linking to subroutines.
— Count register (CTR). Holds a loop count that can be decremented during execution of
appropriately coded branch instructions. CTR also provides the branch target address for the
branch conditional to count register (bcctr, bcctrl) instructions.
— The time base facility (TB) consists of two 32-bit registers, time base upper (TBU) and time
base lower (TBL). User-level software can read (but not write) to these two registers.
— SPRG4–SPRG7. Software-use special-purpose registers (SPRGs). SPRG4–SPRG7 are read
only by user-level software. The e200z3 does not allow user-mode access to SPRG3. Book E
defines such access as implementation-dependent.
— USPRG0. User-software-use SPR USPRG0, which is read-write accessible to user-level
software.
•
Supervisor-level registers, which are control and status registers accessible to supervisor-level
software. An operating system might use these registers for configuration, exception handling, and
other operating system functions:
— Processor control registers
– Machine state register (MSR). Defines the state of the processor. The MSR can be modified
by the move to machine state register (mtmsr), system call (sc), and return from interrupt
(rfi, rfci, rfdi) instructions. It can be read by the move from machine state register (mfmsr)
instruction. When an interrupt occurs, the contents of the MSR are saved to one of the
machine state save/restore registers (SRR1, CSRR1, DSRR1).
– Processor version register (PVR). A read-only register that identifies the version (model)
and revision level of the PowerPC processor.
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