Long-Range GasP with Charge Relaxation

GasP circuit modules communicate handshake signals in two directions over a single state wire. The 2008 Infinity test chip demonstrated GasP in 90 nm CMOS operating at four giga data items per second, but revealed that state wires about 5000 lambda long retard operation by about 10%. Simulations reported in this paper show that GasP modules will tolerate surprisingly long state wires, albeit at reduced throughput. The modules appear to operate correctly with state wires whose delay exceeds the drive time. With such long wires, the receiving module waits until passive distribution of charge brings the wire within range of the receiver's switching threshold. Having put enough charge into the wire, or vice-versa removed enough charge from it,the sending module may proceed with its next task. This result applies equally to other single-track signaling methods.This behavior calls for a new kind of relative timing constraint to address when the wire charging or discharging process may cease rather than when the signal reaches the far end of the wire.