Vector +Floating Point Implementation Tutorial

ARM provide a hardware floating point coprocessor that provides floating +point computation that is fully compliant with IEEE Std 754-1985.

To support a coprocessor, you need to:

Configure the Kernel +to use VFP through a macro setting in the Variant.
Configure the ROM to +include a Kernel extension to support IEEE-without-exceptions mode.
Configure the ROM to +include VFP support libraries.
Port the User Library +to implement its Math class functions to use VFP-enabled +functions. This is described in the Math +Class Port Tutorial.

Variant configuration

Define the macro __CPU_HAS_VFP in +the base port’s variant.mmh. This macro forces the inclusion +of VFP support when the kernel is re-compiled. As an example, see the Integrator +CM1136 base port, and specifically: ...\integrator\core\cm1136\variant.mmh. +When the kernel is re-compiled, VFP support is included.

HAL configuration

Add the HAL attribute for VFP +to your base port's config.hcf file, by adding the following +line to this file:

EHardwareFloatingPoint = GetHardwareFloatingPoint

As an example, see the Integrator CM1136 base port, and specifically: ...\integrator\core\cm920\hal\config.hcf

See +also Creating the Config +& Values files in the HAL Port +Implementation Tutorial for more information.

IEEE-without-exceptions +mode

Symbian platform supports two execution modes :

+ + + +

RunFast

In this mode, denormalised numbers, i.e. those outside the range +of normal floating point values, are treated as zero, and a default NaN (Not +a Number) value is used for all NaN situations regardless +of the inputs.

+ + +

IEEE-without-exceptions

In this mode, denormalised numbers are treated as their actual values, +and the IEEE754-mandated values for NaN s are used.

The +floating point model mandated by the Java specification is identical to this +mode, and means that this mode is sufficient to implement a VFP-accelerated +JVM.

+ + + +

NOTE: There may be some applications that depend on the correct +handling of calculations involving, or resulting in, very small numbers; for +such applications, RunFast mode may not be appropriate.

RunFast mode

For RunFast execution +mode, nothing else needs to be implemented, and no extra components need to +be added to the ROM.

IEEE-without-exceptions +mode

For IEEE-without-exceptions mode, you need +to include the kernel extension evfp.dll in the ROM image +by adding the following line into the .iby or .oby file +for your port:

extension[VARID]=KERNEL_DIR\DEBUG_DIR\evfp.dll \sys\bin\evfp.dll

As an example, see the Integrator CM1136 base port, and specifically: ...\integrator\core\cm1136\rom\base_integrator1136.iby

Note:

This is the default +execution mode.
It is possible to switch +between this execution mode and the RunFast execution mode.
evfp.dll is +built using ARM's VFP support code and can only be built using the RVCT tool +chain.

VFP-enabled +floating port support libraries

Symbian platform provides both +the VFP version and the non-VFP version of the floating point support functions. +You choose the VFP version when you build your ROM image by specifying the VFPHELPERS macro +to BUILDROM. +This causes the ROM building tool chain to replace the following three DLLs:

drtaeabi.dll
dfpaeabi.dll
dfprvct2_2.dll

There are two ways to specify the VFPHELPERS macro:

by adding the following +line into the header.iby file for your port:
#define VFPHELPERS
You +use this technique to permanently include the VFP versions in your ROM image.
by passing VFPHELPERS as +a pre-processor argument using the -D option when invoking BUILDROM, i.e. :

BUILDROM +-DVFPHELPERS ...

You use this technique if you only want +to include the VFP versions for a specific ROM image, for example, when testing.

If you use the first technique, you can still provide non-VFP versions +for a specific ROM image by passing NOVFPHELPERS as a pre-rpocessor +argument using the -D option when invoking BUILDROM, +i.e. :

BUILDROM -DNOVFPHELPERS ... +

In effect, you are overriding the definition in the header.iby file.

For +example, see the Integrator CM1136 base port, and specifically: ...\integrator\core\cm1136\rom\header.iby