External crystal oscillator cycle duration and variation tracking
AssigneeHewlett-Packard Development Company, L.P.
InventorsGary T. Brown, Vincent C. Skurdal
Life of this patent
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Abstract
Secure circuitry of an integrated circuit detects a duration of a clock cycle of a crystal oscillator external to the integrated circuit, using a digital ring oscillator internal to the integrated circuit and having a higher frequency than the crystal oscillator. The secure circuitry calculates a variation in the duration of the clock cycle. In response to the duration being greater than a maximum duration limit, the duration being less than a minimum duration limit, and/or the variation being greater than a maximum variation limit, the secure circuitry performs an action.
Claims13
A method comprising:
- detecting, a duration of a clock cycle of a crystal oscillator using a digital ring oscillator wherein;
- the digital ring oscillator is internal to an integrated circuit and the crystal oscillator is external to the integrated circuit;
- the integrated circuit is inaccessible by components of a computing device except through an oscillator interface and a monitoring interface;
- and
- the digital ring oscillator has a higher frequency than the crystal oscillator;
- calculating, based on secure circuitry of the integrated circuit receiving a signal from the digital ring oscillator and receiving a signal from the oscillator interface, a variation in the duration of the clock cycle;
- increasing the duration in response to a rising edge of the digital ring oscillator;
- and
- setting a most recent duration to the duration, and resetting the duration in response to the rising edge of the crystal oscillator.
A non-transitory computer-readable data storage medium storing program code executable by secure circuitry of an integrated circuit inaccessible by components of a computing device except through an oscillator interface and a monitoring interface to:
- receive a signal from a crystal oscillator external to the integrated circuit via the oscillator interface;
- track a duration of a clock cycle of the crystal oscillator external to the integrated circuit, using a digital ring oscillator internal to the integrated circuit and having a higher frequency than the crystal oscillator by:
- in response to a rising edge of the digital ring oscillator, increasing the duration;
- and
- in response to the rising edge of the crystal oscillator, setting a most recent duration to the duration, and resetting the duration;
- and
- track a variation in the duration of the clock cycle.
An integrated circuit comprising:
- an oscillator interface on which a crystal oscillator external to the integrated circuit is monitored;
- a digital ring oscillator having a frequency greater than the crystal oscillator;
- a monitoring interface on which alerts are triggered responsive to monitoring the crystal oscillator;
- and
- secure circuitry to:
- track a duration of a clock cycle of the crystal oscillator using the digital ring oscillator by:
- in response to a rising edge of the digital ring oscillator, increasing the duration;
- in response to the rising edge of the digital ring oscillator or in response to the rising edge of the crystal oscillator, setting a maximum duration to the duration if the maximum duration is less than the duration;
- and
- in response to the rising edge of the crystal oscillator, setting a minimum duration to the duration if the minimum duration is greater than the duration, setting a most recent duration to the duration, and resetting the duration;
- and
- track a variation in the duration of the clock cycle;
- in response to the duration being greater than a maximum duration limit, trigger an underclocking alert;
- in response to the duration being less than a minimum duration limit, trigger an overclocking alert;
- and
- in response to the variation being greater than a maximum variation limit, trigger a glitching alert, wherein, the integrated circuit is accessible only by the oscillator interface and the monitoring interface.
Dependencies are inferred from the claim text.