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Device Performance Optimization
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
33-13
33.4.3
Hardware Single Precision Floating Point
The SPE-APU also supports 32-bit IEEE®-754 single-precision floating-point formats, and supports
vector and scalar single-precision floating-point operations. Most compiler vendors include libraries that
can emulate floating point functionality. However, by specifying the correct compiler options, the single
precision floating point instructions may be used.
To enable use of hardware floating point the MSR[SPE] field must be set. Refer to
for register details.
33.4.4
Variable Length Encoding
In addition to the base Power Architecture Book E instruction set support, the e200z7 core also implement
the VLE (variable-length encoding) APU, providing improved code density. The VLE-APU can be viewed
as a supplement to the existing Power Architecture instruction set that can be conditionally applied to a
portion of, or an entire application for which improved code density is desired.
Using it is straightforward:
1. Select the appropriate compiler target and option to generate VLE code.
2. Configure the Memory Management Unit (MMU) to specify VLE attributes for the relevant MMU
pages. Refer to the register description in
Section 33.3.6, Memory Management Unit (MMU)
VLE-enabled cores run both Book E and VLE instruction encodings on a page by page basis, with pages
defined by the MMU. The reduction is code size is typically between 25% & 30%.
23
FE
Floating-Point Available
24–25
Reserved
26
IS
Instruction Address Space
27
DS
Data Address Space
28
Reserved
29
PMM
PMM Performance Monitor Mark
30
RI
Recoverable Interrupt
31
Reserved
Table 33-5. MSR Register Field Descriptions (continued)
Field
Description
Содержание PXR4030
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