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422
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
Chapter 3:
User Programming Model
R
shows the operation of the multiply low-halfword to word
instructions.
Floating-Point Emulation
The PPC405 is an integer processor and does not support the execution of floating-point
instructions in hardware. System software can provide floating-point emulation support
using one of two methods.
The preferred method is to supply a call interface to subroutines within a floating-point
run-time library. The individual subroutines can emulate the operation of floating-point
instructions. This method requires the recompilation of floating-point software in order to
add the call interface and link in the library routines.
Alternatively, system software can use the program interrupt. Attempted execution of
floating-point instructions on the PPC405 causes a program interrupt to occur due to an
illegal instruction. The interrupt handler must be able to decode the illegal instruction and
call the appropriate library routines to emulate the floating-point instruction using integer
instructions. This method is not preferred due to the overhead associated with executing
the interrupt handler. However, this method supports software containing PowerPC
floating-point instructions without requiring recompilation. See
, for more information.
Processor-Control Instructions
In user mode, processor-control instructions are used to read from and write to the
condition register (CR) and the special-purpose registers (SPRs). Instructions that access
the time base are also considered processor-control instructions, but are discussed
separately in
.
Multiply Low-Halfword to Word Unsigned
Instructions
r
D is loaded with the unsigned product (
r
A[16:31])
×
(
r
B[16:31]).
mullhwu
Multiply Low Halfword to Word
Unsigned
CR0 is
not
updated.
r
D,
r
A,
r
B
mullhwu.
Multiply Low Halfword to Word
Unsigned and Record
CR0 is updated to reflect the result.
Table 3-48:
Multiply Low-Halfword to Word Instructions
(Continued)
Mnemonic
Name
Operation
Operand
Syntax
Figure 3-36:
Multiply Low-Halfword to Word Operation
UG011_28_033101
r
D
0
31
r
A
0
31
16
r
B
0
31
15
×
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