Patent Application
20070173215
Embodiments of the invention relate to a physical layer interface of a computing system. More particularly, embodiments of the invention relate to techniques for detecting an in-band reset signal in a physical layer interface of a computing system.
Computing systems may be reset, or include one or more components or sub-systems that may be reset, by an external signal received via a physical layer interface. On technique for communicating an in-band reset is to halt a clock signal provided to a physical layer interface. Currently, detection of absence of a clock signal is accomplished using relatively complex analog circuitry.
Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements.
In the following description, numerous specific details are set forth. However, embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.
Source system 180 may include any type of electronic or other components that allow signals 190 and clock signal 195 to be transmitted to receiving system 100. Physical layer interface 120 may include the physical connection to the signal lines that carry signals 190 and clock signal 195. Physical layer interface 120 may include any type of interface circuitry known in the art in addition to the various embodiments of circuitry to detect in-band resets as described herein.
In one embodiment, physical layer interface 120 may provide signals 130 as well as reset signal 125 to control circuitry 140. Control circuitry 140 may include any type of circuitry to provide functionality in response to signals 130 and/or reset signal 125. Additional and/or different components may also be included in receiving system 100.
In one embodiment, internal clock counter 210 may be coupled to receive an internal clock signal. The internal clock signal may be generated by, for example, a circuit in a component in which the digital circuitry of
In one embodiment, internal clock counter 210 may enable the output signal for periods of time corresponding to a pre-selected number (e.g., 20, 25, 50) of internal clock signal cycles. The number of clock cycles for which the output signal is enabled may be selected based, at least in part, on, for example, the ratio of the internal clock signal to the external clock signal, the slack specified between the internal clock signal and the external clock signal, the asynchronous nature of the clock domains, etc. In one embodiment, the internal clock signal is approximately 2.0 GHz and the external clock signal is approximately 3.2 GHz.
When external clock counter 220 is enabled by the output signal from internal clock counter 210, external clock counter 220 may count cycles of the external clock signal. Because the frequency of the internal clock signal is known, external clock counter 220 is enabled for a known period of time. During that known period of time, if the external clock signal is functional a known number of clock cycles will be counted.
In one embodiment, external clock counter 220 may generate a multi-bit output signal that corresponds to the number of external clock signal cycles counted during the time period that external clock counter 220 is enabled by the output signal of internal clock counter 210. Comparison circuitry 230 may compare the multi-bit output signal from external clock counter 220 to a pre-selected range (e.g., 28 to 36, 30 to 33). In one embodiment, if the output of external clock counter 220 is within the expected range, the external clock signal is considered operational. However, if the output of external clock counter 220 is not within the expected range, the external clock signal may be considered suspended and a reset signal may be generated. The reset signal may be used, for example, to reset a point-to-point link connection, or for another purpose.
Cycles of the first clock signal may be counted, 320. In one embodiment, a digital counter may be used to count cycles of the first clock signal, which may be an internal clock signal or any other reference clock signal having a known frequency. The counter may generate an output signal corresponding to windows of time determined in terms of the first clock signal. For example, the output signal may be asserted for a pre-selected number of cycles of the first clock signal, deasserted for a period of time and then asserted again for the pre-selected number of cycles of the first clock signal.
Counting of cycles of the second clock signal may be selectively enabled, 330. In one embodiment, when the output signal described above is asserted, cycles of the second, or external clock signal, may be counted. In one embodiment, cycles of the second clock signal may be counted using a digital counter that may generate a multi-bit output signal corresponding to a number of clock cycles of the second clock signal counted when counting is enabled.
The number of cycles of the second clock signal counted may be compared with a range of expected number of clock cycles, 340. Because the time period for which counting cycles of the second clock signal is known and the frequency of the second clock signal is known, a number of expected clock cycles may be determined. If the number of counted clock cycles does not fall within an acceptable range, a reset signal may be generated, 350.
Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.
