AUTOMATIC SELECTION OF ON-CHIP CLOCK IN SYNCHRONOUS DIGITAL SYSTEMS
First Claim
1. A synchronous digital system comprised on a chip, the synchronous digital system comprising:
- synchronous digital logic configured to operate using a primary clock signal;
an on-chip clock signal generator configured to generate a first clock signal independent of an external clock signal received by the synchronous digital system; and
clock signal selector circuitry configured to select between a plurality of clock signals for use as the primary clock signal, wherein the plurality of clock signals comprises the first clock signal and a signal dependent on the external clock signal, wherein the clock signal selector circuitry is further configured to;
when a clock selection override signal indicates normal operation, select between the plurality of clock signals based at least in part on the contents of a software-configurable register; and
when the clock selection override signal indicates a condition requiring selection of a clock signal generated on-chip for use as the primary clock signal, select the first clock signal.
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Accused Products
Abstract
Embodiments of a synchronous digital system are disclosed that may include generation of clock and synchronization signals. Any of a plurality of available clock signals may be selected for use as a primary clock, without causing clock-induced errors in the synchronous digital system. A clock signal generated on-chip with the synchronous digital system may be automatically selected in response to detecting a condition indicating that use of a local clock may be necessary. Such conditions may include detection of tampering with the synchronous digital system. If an indication of tampering is detected, security measures may be performed.
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Citations
16 Claims
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1. A synchronous digital system comprised on a chip, the synchronous digital system comprising:
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synchronous digital logic configured to operate using a primary clock signal; an on-chip clock signal generator configured to generate a first clock signal independent of an external clock signal received by the synchronous digital system; and clock signal selector circuitry configured to select between a plurality of clock signals for use as the primary clock signal, wherein the plurality of clock signals comprises the first clock signal and a signal dependent on the external clock signal, wherein the clock signal selector circuitry is further configured to; when a clock selection override signal indicates normal operation, select between the plurality of clock signals based at least in part on the contents of a software-configurable register; and when the clock selection override signal indicates a condition requiring selection of a clock signal generated on-chip for use as the primary clock signal, select the first clock signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of avoiding clock signal errors in a synchronous digital system comprised on a chip, the method comprising:
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providing a first clock signal as a primary clock for the synchronous digital system, wherein the first clock signal is dependent upon an external clock signal received by the synchronous digital system; receiving a clock selection override signal indicating a condition requiring selection of a clock signal generated on-chip for use as the primary clock; selecting, in response to the receiving, a second clock signal as the primary clock, wherein the second clock signal is generated by an on-chip clock signal generator independent of the external clock signal. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification