vxworks programmer's guide.pdf - DAQ Plone Site

E
MIPS R3000, R4000, R4650
E.4 Architecture Considerations
This section describes the following characteristics of the MIPS architecture that
you should keep in mind as you write a VxWorks application:
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Gprel addressing
Reserved registers
Floating-point support
Interrupts
Virtual memory mapping
64-bit support
Memory layout
Gprel Addressing
The VxWorks kernel uses gprel (gp-relative) addressing. However, the VxWorks
module loader cannot dynamically load tasks that use gprel addressing.
To keep the loader from returning an error, compile application tasks with the -G 0
option. This option tells the compiler not to use the global pointer.
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Reserved Registers
Registers k0 and k1 are reserved for VxWorks kernel use, following standard MIPS
usage. The gp register is also reserved for the VxWorks kernel, because only the
kernel uses gprel addressing, as discussed in above. Avoid using these registers in
your applications.
Floating-Point Support
R4650
For the R4650, single precision hardware floating-point support is included by
INCLUDE_HW_FP (which is included by default in the project facility VxWorks
view). Double precision floating-point support is provided by software emulation
when you use -msoft-float. (Note that INCLUDE_SW_FP is not required with
-msoft-float for the R4650.)
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