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Multimedia Support

Carnegie Mellon University Computer Science Department Computer Architecture F’01. Multimedia Support. v. Jernej Barbic Overview of multimedia and processors Luis von Ahn An Example: AltiVec. Multimedia means…. Still images, Audio, Video.

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Multimedia Support

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  1. Carnegie Mellon University Computer Science Department Computer Architecture F’01 Multimedia Support v Jernej Barbic Overview of multimedia and processors Luis von Ahn An Example: AltiVec.

  2. Multimedia means… • Still images, • Audio, • Video. Creating, displaying, playing, manipulating, compressing, decompressing Each of these require different type of CPU operations.

  3. Typical multimedia formats • JPEG • MP3 • MPEG • MPEG-4 just released • Decompression significantly slower than compression • DVD

  4. Multimedia operations are a bottleneck In this presentation, we focus on this • CPUs cannot compute fast enough • Memory/disk latencies too large • Network bandwidth too low • Playing 352 x 242 x 24 bit MPEG video requires a T1 line (1.5 Mbps)

  5. The majority of CPU multimedia operations are: • Matrix multiplications, inner products of vectors • FFT, DCT (discrete cosine transformation) • JPEG, MPEG, MP3 • Multiply-accumulate instructions • Calculating the sum of several products (e.g. in an inner product) • Overflow problems • Product of two 8-bit numbers is a 16-bit number • Some multimedia architectures incorporate special hardware to deal with overflows (saturated arithmetics) • Single precision floating point operations • Single precision = 32-bit • geometry 3D processing

  6. The majority of CPU multimedia operations are (contd.): • Calculating the sum of absolute differences • MPEG compression: detecting motion • Implemented in hardware only in Alpha’s MVI detecting motion

  7. Multimedia features of modern processors • PS (paired single) floating point (fp) format • Problem: typical fp registers are 64-bit, but a lot of data is 32-bit • Solution: • pack two 32-bit single precision fp numbers into a 64-bit register • provide hardware to operate on both 32-bit components in parallel • Many geometric operations require only single fp precision • Useful also for non-multimedia tasks (scientific computing) • Using PS increases performance by a factor of two

  8. Multimedia features of modern processors (contd.) • SIMD (single instruction, multiple data) • SIMD is the integer version of PS • Divide 64-bit integer registers into eight bytes (8 bit) or four half-words (16 bit) • Operate on this data in parallel • Parallel arithmetic instructions • Instructions to store, load, rearrange individual bytes

  9. Multimedia architectures • Alpha: MVI (motion-video instructions) multimedia extension • Alphas are fast and don’t need extensive multimedia additions • Fast video (MPEG) compression enabled in MVI • Limited SIMD support, little parallel arithmetic instructions, … • but already fast without them. • Special “motion detecting instruction”: PERR Ra, Rb, Rc Calculates

  10. Multimedia architectures (contd.) • MIPS V • Fully support SIMD and PS • Instructions add little to the complexity of circuitry • MIPS MDMX • More extensive than MIPS V • Supports 32 “media” registers • Media registers mapped to 64-bit floating point registers • SIMD formats: oct-byte (8x 8-bit), quad-half (4x 16-bit) • Saturated arithmetics: avoids underflows and overflows • Wide 192-bit accumulator to support extensive multiply-accumulate instructions

  11. Multimedia architectures (contd.) • HP • Intel • MMX • Sun • VIS (visual instruction set) • AltiVec

  12. Multimedia for the PowerPC: AltiVec Branch Unit Integer Unit Floating-Point Unit Vector Unit Memory

  13. Multimedia for the PowerPC: AltiVec • 32 vector registers • 162 new instructions • 128-bit vectors: 16 values 8 values 4 values

  14. AltiVec: Vector Permute 01 04 08 00 1F 15 09 0A 05 1F 02 03 07 0D 0B 0E VC VB 1 0 VA 0 1 2 3 4 5 6 7 8 9 A B C D E F VT vperm VT, VA, VB, VC

  15. AltiVec: Other Instructions • Vector Inner Product • Vector Merge • Vector Comparisons • Multiply Accumulate

  16. Does This Really Help? Time (Times are normalized)

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