Transition Inversion based Low Power Data Coding Scheme for Buffered Data Transfer

Transition Inversion based Low Power Data Coding Scheme for Buffered Data Transfer

1 Suhasini Parunandi, 2 P. Anitha,
1 PG Student
2 Assistant Professor
Malla Reddy College of Engineering (MRCE) Dulapally ,Telangana ,India

Abstract:- In this work the authors propose a data coding protocol that leads to power reduction for block data transfer in off-chip buses. I/O pads driving off-chip buses contribute to a major portion of power dissipation in chips. Also, block data transfer is preferred in most systems like caches, DMA etc. In this proposed work, the prior knowledge of the block of data to be transmitted, when it is stored in the buffer, is exploited in a serial fashion to reduce transitions on every bus line. Statistical analysis shows up to 31.9% reduction in transitions. Benchmark results show that it leads to 29% reduction in power consumption. The technique provides added error detection on the lines of parity bit technique, with similar average error detection capability.

1. INTRODUCTION
Increased integration and higher operating frequencies compound the problem of power dissipation in VLSI chips. One of the main contributors to power consumption is switching activity on the high-capacitance lines of an interconnection system, especially off-chip buses. Buses constitute an important resource for addressing and data transfer in the implementation of most electronic systems. The fact that the power consumed at the I/O pads accounts for a significant fraction of the total power consumed in VLSI systems has been independently established by many researchers [1-3].
Error detection is also of equal importance, as buses are more prone to error due to temperature variations, interference from neighboring sources, and ageing etc. Thus a low power data coding scheme supporting error detection is desired. Existing techniques make use of the data as it is placed on to the bus. This leads to a delay which can severely affect the operating frequency of the circuit. The proposed encoding
technique, which is based on serial transition inversion, works on blocks of data for power reduction in off-chip buses. Numerous bus transmission protocols deal with blocks of data rather than individual data words. This is evident in DMA transfers and cache lines which are widely used in computer systems. In block data transfer the latency in data coding can be hidden since the block will be transmitted only after it is filled up. This brings the pipeline approach to the coding technique. Since Off- chip buses consume more power, keeping the encoding circuitry before the I/O pad reduces power consumed by it. The proposed technique is also called transition inversion in the following sections

2. RELATED WORK
One of the most often cited encoding methods is the bus-invert method [1]. Bus-invert selects between the original and the inverted pattern in a way that minimizes the switching activity on the bus. The resulting patterns together with an extra bus line (to notify whether the address or its complement has been sent) are signaled over the bus. Musoll et al. proposed the working zone method [3]. Their method takes advantage of the fact that data accesses tend to remain in a small set of working zones. Other encoding techniques include Asymptotic Zero-Transition Encoding [2], Gray coding (mostly for addresses), and other application specific encoding techniques [9,10]. Most of the existent techniques make use of the repeating patterns in address buses to reduce address bus transitions [6,8,9]. Frequent Value encoding (FVE) is another technique proposed in [13] also results in a significant reduction in transitions, but has not been considered here, due to the overhead involved.
There is no existent literature on bus coding methodologies for block data transfer, other than Serial Bus Invert [14], which encodes blocks of data rather than individual data words. Also a transition inversion