Context-Independent Codes for Off-Chip Interconnects

This paper introduces the concept of context-independent coding using frequency-based mapping schemes in order to reduce off-chip interconnect power consumption. State-of-the-art context-dependent, double-ended codes for processor-SDRAM off-chip interfaces require the transmitter and receiver (memory controller and SDRAM) to collaborate using current and previously transmitted values to encode and decode data. In contrast, the memory controller can use a context-independent code to encode data stored in SDRAM and subsequently decode that data when it is retrieved, allowing the use of commodity memories. In this paper, a single-ended, context-independent code is realized by assigning limited-weight codes using a frequency-based mapping technique. Experimental results show that such a code can reduce the power consumption of an uncoded off-chip interconnect by an average of 30% with less than a 0.1% degradation in performance.