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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
Programming Model
Page 118 of 377
gx_02.fm.(1.2)
March 27, 2006
output the 4-bit resource ID (RID) field located in the EAR. The eciwx instruction also loads a word from the
data bus that is output by the special device. For more information about the relationship between these
instructions and the system interface, see Chapter 7, Signal Descriptions, on page 249.
2.3.6 PowerPC OEA Instructions
The PowerPC operating environment architecture (OEA) includes the structure of the memory-management
model, supervisor-level registers, and the exception model. Implementations that conform to the OEA also
adhere to the UISA and the VEA. This section describes the instructions provided by the OEA.
2.3.6.1 System Linkage Instructions—OEA
This section describes the system linkage instructions (see Table 2-40). The user-level sc instruction lets a
user program call on the system to perform a service and causes the processor to take a system-call excep-
tion. The supervisor-level rfi instruction is used for returning from an exception handler.
2.3.6.2 Processor Control Instructions—OEA
This section describes the processor control instructions used to access the MSR and the SPRs. Table 2-41
lists instructions for accessing the MSR.
The OEA defines encodings of mtspr and mfspr to provide access to supervisor-level registers. The instruc-
tions are listed in Table 2-42.
Encodings for the architecture-defined SPRs are listed in Table 2-33 on page 109. Encodings for 750GX-
specific, supervisor-level SPRs are listed in Table 2-34 on page 112. Simplified mnemonics are provided for
mtspr and mfspr in Appendix F, “Simplified Mnemonics” in the PowerPC Microprocessor Family: The
Programming Environments Manual. For a discussion of context synchronization requirements when altering
certain SPRs, see Appendix E, “Synchronization Programming Examples” in the PowerPC Microprocessor
Family: The Programming Environments Manual.
Table 2-40. System Linkage Instructions—OEA
Name Mnemonic Syntax Implementation Notes
System Call sc — The sc instruction is context-synchronizing.
Return from
Interrupt
rfi —
The rfi instruction is privileged and context-synchronizing. For the 750GX, this
means the rfi instruction works its way to the final stage of the execution pipeline,
updates architected registers, and redirects the instruction flow.
Table 2-41. Move-to/Move-from Machine State Register Instructions
Name Mnemonic Syntax
Move-to Machine State Register mtmsr rS
Move-from Machine State Register mfmsr rD
Table 2-42. Move-to/Move-from Special-Purpose Register Instructions (OEA)
Name Mnemonic Syntax
Move-to Special-Purpose Register mtspr SPR,rS
Move-from Special-Purpose Register mfspr rD,SPR