The impact of Mpact 2

Mpact media processors enable powerful, flexible and cost-effective multimedia in a PC. A single chip replaces today's multiboard, multichip solutions for graphics, video, audio, and communications. The architecture combines a high-bandwidth RAMBUS memory, VLIW/SIMD (single instruction, multiple data) processing, standard buses, and software programmability for the cost of a modern graphics chip. Mpact architecture uses a modified VLIW style with two RISC-like instructions per VLIW. The instructions are either executed sequentially or concurrently based on a tag in the VLIW. Classical VLIW suffers from low code density due to unused instruction fields, but the Mpact modified VLIW has the same code density as RISC instructions. Additionally, the SIMD instructions improve code density by increasing the work done by each instruction. An 8 byte word size was chosen to balance vector and scalar performance and also to balance data and instruction bandwidth. A 9 bit byte was chosen to represent color-component differences in one byte and to represent 18 bit color or 18 bit audio samples in two bytes. Hardware-dithered rounding of quantization noise allows most audio to be processed in two byte precision. The maximal multiplier precision of 24/spl times/24 was chosen for audio requirements. The article reviews the first-generation Mpact media processor and then describes the multimedia performance goals and architecture of Chromatic's second-generation media processor architecture. It then presents newer modules of the architecture in more detail.