Abstract: Systems and methods are disclosed for phase calibration between clock and data lanes at a data link receiver. In calibration mode, matching signals are transmitted over the clock and data lanes, and a phase offset is measured at the receiver. A phase shifter in one signal path is adjusted to a first phase to obtain a desired phase offset. For operation mode, the phase shifter is set based on the first phase. Embodiments measure phase offset using an XOR gate and use a phase interpolator as the phase shifter. Embodiments with multiple data lanes apply coarse calibration to a shared clock lane relative to a first data lane, and similar fine calibration to other data lanes. Calibration provides optimum signal-to-noise ratio or timing margin, enabling high transmission speeds at relatively low power. Variations are disclosed.

Abstract: Systems and methods are disclosed for reduced-power serial data links. A clock-forwarded serial link carries a clock lane and one or more data lanes. Every active serial data cycle is accompanied by its own serial clock edge: a clock delay allows the same clock edge to drive data at a transmitter and latch data at a receiver. Power is saved by idling the serial clock when data is not being transmitted. A valid signal can be omitted, providing a space saving. At the destination, similar clock-forwarding and delay enables a single parallel clock edge to drive data to the boundary of its clock domain, e.g. from a deserializer to a FIFO. The data link exhibits zero-cycle entry and exit. Variations with half- or single-cycle entry or exit are disclosed.

Abstract: Systems and methods are disclosed for clock phase calibration between source logic and a coupled serial data link transmitter, enabling low-latency synchronization into the transmitter. In calibration mode, a phase relationship is monitored between a first clock, driving the source logic, and a second clock, tightly synchronized with a serial clock of the data link. The first clock is adjusted to a first phase at which the first and second clocks are aligned. The first clock phase is set for operation mode based on the first phase. Monitoring uses a D-type flip-flop as a phase detector. Adjustment is in steps of half the serial clock period. Variations are disclosed.

Abstract: Systems and methods are disclosed for credit-based flow control of multiple data links using a common reverse channel. The links transfer data from a source to respective buffers at a sink. Credits represent available buffer space. For each data link, a credit counter at the source is decremented as data is transmitted and incremented as the sink returns credits. Reporting logic at the data sink generates a credit report as sink logic retrieves data from the buffer, freeing buffer space. Encoding logic aggregates the credit reports from multiple links for transmission over the common reverse channel to the source, where individual credit reports are extracted and distributed among the links, for update to the respective credit counters. For each link, data transmission pauses when the credit counter decreases to a threshold. Return multiple links' credits over a single reverse channel saves power. Variations are disclosed.

Abstract: A digital signal processor includes analog to digital converters to convert an analog voltage to digital voltage in unit intervals of an analog signal. A decision feedback equalizer (DFE) determines a first level of a digital sum of a digital voltage in a first UI and digital voltages of adjacent UIs (taps). The DFE identifies predetermined sequences of levels of consecutive UIs that include the first level and selects one of the predetermined sequences to decode digital data encoded in the analog signal in the UI. The DSP may be programmable to include taps from UIs that may affect the first UI. The predetermined sequences may include levels of the digital sums of consecutive UIs of the analog signal. The predetermined sequences may be identified in a look-up table based on the first level.