Xilinx Virtex-II Pro PPC405, Руководство пользователя

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March 2002 Release www.xilinx.com 423
Virtex-II Pro™ Platform FPGA Documentation 1-800-255-7778
Processor-Control Instructions
R
Condition-Register Move Instructions
The condition-register move instructions shown in Table 3-49 are used to read and write the
condition register using a GPR as a destination or source register, and for writing a CR field
from the XER register. Not included in this category are other instructions that access the
CR. See
Condition-Register Logical Instructions , page 376 , for information on
instructions used to manipulate bits and fields in the CR. See Conditional Branch Control ,
page 367 , for information on how certain branch instructions use values in the CR as
branch conditions.
mtcrf Field Mask (CRM)
The mtcrf instruction uses an 8-bit field mask (CRM) specified in the instruction encoding
to control which CR fields are loaded from r S. As shown in Figure 3-37 , each bit in CRM
corresponds to one of the 4-bit CR fields, with the most-significant CRM bit corresponding
to CR0 and the least-significant CRM bit corresponding to CR7. When
mtcrf is executed, a
CR field is loaded with the corresponding bits in r S only when the associated CRM mask
bit is set to 1. If the mask bit is cleared to 0, the CR field is unchanged.
Figure 3-38 shows an example of how the CRM field is used. In this example,
CRM = 0b01100100, causing CR1, CR2, and CR5 to be updated with the corresponding bits
in
r S. All remaining CR fields are unchanged.
Table 3-49: Condition-Register Move Instructions
Mnemonic Name Operation
Operand
Syntax
mcrxr Move to Condition Register from XER
The CR field specified by the crf D operand is
loaded with XER[0:3]. The remaining bits in the
CR are not modified. The contents of XER[0:3] are
cleared to 0.
crf D
mfcr Move from Condition Register
r
D is loaded with the contents of CR.
r D
mtcrf Move to Condition Register Fields
CR is loaded with the contents of r S under the
control of a field mask specified by the CRM op-
erand.
CRM,
r S
Figure 3-37: mtcrf Field Mask (CRM) Format
UG011_31_033101
CRM
CR1 CR2 CR3 CR4 CR5 CR6 CR0 CR7
1 2 3 4 5 6 0 7