Design of a 2D DCT/IDCT application specific VLIW processor supporting scaled and sub-sampled blocks

We present an innovative design of an accurate, 2D DCT IDCT processor, which handles scaled and sub-sampled input blocks efficiently. In the IDCT mode, the latency of the processor scales with the size of the input blocks varying from 7 cycles for an 1x1 block to 38 cycles for an 8x8 block. This scalability is possible because the processor has input data dependant control by which it can exploit the reduced computational needs of sub-sampled blocks and blocks of smaller sizes to work in lesser cycles. This is a very useful feature for MPEG and HDTV decoders and has hitherto not been exploited. Clocking at 150 Mhz, the processor satisfies the high sample rate requirement of dual MPEG stream HD decoding with a picture size of 1920 x 1080 at 30 frames per second. Fixed word length and accuracy simulations of our design shows that it conforms to the accuracy specifications of the CCITT standard within a 16 bit data path. A methodology based on architecture level synthesis is used to design the VLIW processor core. The VLIW design exploits the Instruction Level Parallelism present in the DCT/IDCT application, efficiently. The processor core is characterised by an area of 0.834 mm sq. and a frequency of 150 Mhz in 0.18 micron CMOS technology.