Systolic Arrays - Signal Processing Systems - page 1114

for processor-to-processor communication with no external-glue logic. The com-
munication ports remove input/output bottlenecks, and the independent smart DMA
coprocessor is able to relieve the CPU input/output burden.
Each of the six serial communication ports is equipped with a 20 Mbytes/s
bidirectional interface, and separate input and output eight-word-deep FIFO buffers.
Direct processor-to-processor connection is supported by automatic arbitration and
handshaking. The DMA coprocessor allows concurrent I/O and CPU processing for
sustained CPU performance.
The processor features single-cycle 40-bit floating-point and 32-bit integer
multipliers, 512-byte instruction cache, and 8 K bytes of single-cycle dual-access
program or data RAM. It also contains separate internal program, data, and DMA
coprocessor buses for support of massive concurrent input/output (I/O) program and
data throughput.
The TMS 32040 is designed to support general-purpose parallel computation
with different configurations. With six bidirectional serial link ports, it would
directly support a hypercube configuration containing up to 2 6 64 processing

elements. It, of course, also can be easily configured to form a linear or two-
dimensional mesh-connected processor array to support systolic computing.

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6 Recent Developments and Real World Applications

6.1 Block Motion Estimation

Block motion estimation is a critical computation step in every international
video coding standard, including MPEG-I, MPEG-II, MPEG-IV, H.261, H.263,
and H.264. This algorithm consists of a very simple loop body (sum of absolute
difference) embedded in a six-level nested loop. For real time, high definition video
encoding applications, the motion estimation operation must rely on special purpose
on-chip processor array structures that are heavily influenced by the systolic array
concept.
The notion of block motion estimation is demonstrated in Fig. 15 . Totheleft
of this figure is the current frame , which is to be encoded and transmitted from
the encoding end. To the right is the reference frame , which has already been
transmitted and reconstructed at the receiver end. The encoder will compute a copy
of this reconstructed reference frame for the purpose of motion estimation. Both
the current frame and the reference frame are divided into macro-blocks as shown
with dotted lines. Now focus on the current block , which is the shaded macro-block
at the second row and the fourth column of the current frame. The goal of motion
estimation is to find a matching macro-block in the reference frame, in the vicinity
of the location of the current block such that it resembles the current block in the
current frame. Usually, the current frame and the reference frame are separated by a
couple of frames temporally, and are likely to contain very similar scene. Hence,