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97 lines
4.0 KiB
XML
97 lines
4.0 KiB
XML
<!--
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Copyright (c) 2019 OpenPOWER Foundation
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<chapter version="5.0" xml:lang="en" xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="section_intro">
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<!-- Chapter Title goes here. -->
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<title>Introduction to Vector Programming on POWER</title>
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<section>
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<title>A Brief History</title>
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<para>
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The history of vector programming on POWER processors begins
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with the AIM (Apple, IBM, Motorola) alliance in the 1990s. The
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AIM partners developed the Power Vector Media Extension (VMX) to
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accelerate multimedia applications, particularly image
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processing. VMX is the name still used by IBM for this
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instruction set. Freescale (formerly Motorola) used the
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trademark "AltiVec," while Apple at one time called it "Velocity
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Engine." While VMX remains the most official name, the term
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AltiVec is still in common use today. Freescale's AltiVec
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Technology Programming Interface Manual (the "AltiVec PIM") is
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still available online for reference (see <xref
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linkend="VIPR.intro.links" />).
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</para>
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<para>
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The original VMX specification provided for thirty-two 128-bit
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vector registers (VRs). Each register can be treated as
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containing sixteen 8-bit character values, eight 16-bit short
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integer values, four 32-bit integer values, or four 32-bit
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single-precision floating-point values (the "VMX data types").
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Furthermore, the integer data types have signed, unsigned, and
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boolean variants. An extensive set of arithmetic, logical,
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comparison, conversion, memory access, and permute class
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operations were specified to operate on these registers.
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</para>
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<para>
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The AltiVec PIM documents intrinsic functions to be used by
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programmers to access the VMX instruction set. Because similar
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operations are provided for all the VMX data types, the PIM
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provides for overloaded intrinsics that can operate on different
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data types. However, such function overloading is not normally
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acceptable in the C programming language, so compilers compliant
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with the AltiVec PIM (such as <code>gcc</code> and
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<code>clang</code>) were required to add special handling to
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their parsers to permit this. The PIM suggested (but did not
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mandate) the use of a header file,
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<code><altivec.h></code>, for implementations that provide
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AltiVec intrinsics. This is common practice for all compliant
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compilers today.
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</para>
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<para>
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The first chips incorporating the VMX instruction set were
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introduced by Freescale in 1999, and used primarly in Apple
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desktop computers. IBM's last desktop CPU (the PowerPC 970)
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also included AltiVec support, and was used in the Apple
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PowerMac G5. IBM initially omitted support for VMX from its
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server-class computers, but added support for it in the POWER6
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server family.
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</para>
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<para>
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Next talk about VSX introduced for P7. Changes in registers and
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types.
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</para>
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<section>
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<title>Little-Endian Linux</title>
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<para>
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Yes, it caused a lot of problems. See chapter on this.
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</para>
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</section>
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</section>
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<section>
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<title>The Unified Vector Register Set</title>
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<para>filler</para>
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</section>
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<section xml:id="VIPR.intro.links">
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<title>Useful Links</title>
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<para>filler</para>
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</section>
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</chapter>
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