Move To/From Condition Register Instructions; System Linkage Lnstruction-Uisa - IBM PowerPC 604 User Manual

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2.3.4.5 System Linkage lnstruction-UISA
This section describes the System Call (sc) inshllction that pennits a program to call on the
system to perform a service. See also Section 2.3.6.1, "System Linkage
lnshllctions---OEA," for additional information.
Table 2·32. System Linkage lnstructlon-UISA
Name Mnemonic Operand Syntax
System Call
SC
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2.3.4.6 Processor Control lnstructions-UISA
Processor control insbllctions are used to read from and write to the condition register
(CR), machine state register (MSR), and special-purpose registers (SPRs). See
Section 2.3.5.1, "Processor Control lnshllctions-VEA," for the mftb inshllction and
Section 2.3.6.2, "Processor Control lnsbllctions---OEA," for information about the
insbllctions used for reading from and writing to the MSR and SPRs.
2.3.4.6.1 Move to/from Condition Register Instructions
Table 2-33 summarizes the insbllctions for reading from or writing to the condition
register.
Table 2-33. Move to/from Condition Register Instructions
Name Mnemonic Operand Syntax
Move to Condition Register Fields mtcrf CRM,rS
Move to Condition Register from XER mcrxr crfD
Move from Condition Register mfcr rD
Note that the performance of the mtcrf insbllction depends greatly on whether only one
field is being
~ccessed
or either no fields or multiple fields are accessed as follows:
• Those mtcrf insbllctions that update only one field are executed in either of the
SCIUs and the CR field is renamed as with any other SCIU insbllction.
• Those mtcrf inshllctions that update either multiple fields or no fields are dispatched
to the MCIU and a count/link scoreboard bit is set. When that bit is set, no more
mtcrf inshllctions of the same type, mtspr inshllctions that update the count or link
registers, branch insbllctions that depend on the condition register and CR logical
insbllctions can be dispatched to the MCIU. The bit is cleared when the mtctr,
mtcrf, or mtlr inshllction that the bit is executed.
2-46 PowerPC 604 RISC Microprocessor User's Manual