System and method for detecting FRO locking

• US 9,594,541 B2
• Filed: 01/06/2009
• Issued: 03/14/2017
• Est. Priority Date: 01/06/2009
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Inside Secure SA
• Inventors: Verschueren, Ad
• Primary Examiner(s): MILLER, VIVA L
• Application Number:
  US12/319,308
• Publication Number:
  US 20100171560A1
• Time in Patent Office: 2,989 Days
• Field of Search: 708/251
• US Class Current: 1/1
• CPC Class Codes: G06F 7/58 Random or pseudo-random number generators
• CPC Class Codes: G06F 7/588 Random number generators, i.e. based on natural stochastic processes
• CPC Class Codes: H03K 3/84 Generating pulses having a predetermined statistical distribution of a parameter, e.g. random pulse generators

Abstract

The detection of locking of a free running oscillator (FRO) is disclosed, including taking periodic samples of the FRO output, storing each new sample in a sample storage medium, each time a new sample is stored searching the stored samples for at least one repeating pattern, counting consecutive sampling instances in which a repeating pattern is found, and indicating when the count reaches a preselected threshold number.

Claims

1. A device for detecting locking of a free running oscillator (FRO), comprising:

a sampler configured to take periodic samples of an output of the FRO;

a sample storage medium coupled to the sampler and configured to store a plurality of consecutive samples of the output of the FRO;

a first pattern detector coupled with the sample storage medium, the first pattern detector being configured to, in response to a new sample being stored in the sample storage medium, detect, in the plurality of consecutive samples of the output of the FRO, repeating patterns of a first length;

a second pattern detector coupled with the sample storage medium in parallel with the first pattern detector, the second pattern detector being configured to, in response to the new sample being stored in the sample storage medium, detect, in the plurality of consecutive samples of the output of the FRO, repeating patterns of a second length, the second length being different than the first length;

an error counter coupled with the first pattern detector and the second pattern detector, the error counter being configured to count instances of detected repeating patterns;

a threshold detector coupled to the error counter, the threshold detector being configured to output a FRO lock indication signal when the error counter reaches a preselected number of instances of detected repeating patterns, the preselected number being greater than or equal to one; and

a FRO adjuster configured to adjust the FRO in response to the FRO lock indication signal.

2. The device of claim 1, wherein the device is embodied on an application specific integrated circuit (ASIC).

3. The device of claim 1, further comprising a data storage configured to store an indication that the preselected number of instances of detected repeating patterns was detected.

4. The device of claim 1, further comprising an alarm generator configured to generate an alarm when the threshold detector indicates the preselected number of instances of detected repeating patterns has been reached.

5. The device of claim 1, wherein adjusting the FRO includes at least one of restarting the FRO, shutting down the FRO, and changing an operating frequency of the FRO.

6. The device of claim 1, further comprising a threshold level selector configured to change the preselected number.

7. The device of claim 1, wherein the sample storage medium includes a shift register.

8. The device of claim 1, wherein:

detecting, by the first pattern detector or the second pattern detector, repeating patterns includes comparing a respective number of most recent samples of the plurality of consecutive samples of the output of the FRO with a same number of immediately preceding samples of the plurality of consecutive samples of the output of the FRO, and

incrementing the error counter includes incrementing the error counter when at least one of the first pattern detector and the second pattern detector determines that a pattern of the most recent samples is the same as a pattern of the immediately preceding samples.

9. The device of claim 8, wherein the error counter is configured to reset to zero when neither of the first pattern detector and the second pattern detector detect a repeating pattern in response to the new sample being stored in the sample storage medium.

10. The device of claim 1, wherein an operating frequency of the FRO is greater than or equal to one-half a frequency at which the sampler takes the periodic samples of the output of the FRO.

11. A method of detecting locking of a Free Running Oscillator (FRO), the method comprising:

periodically sampling an output of the FRO at a sampling frequency;

storing a plurality of consecutive samples of the output of the FRO in a sample storage medium;

in response to a new sample being stored;

detecting, with a first pattern detector, repeating patterns of a first length in the plurality of consecutive samples of the output of the FRO; and

detecting, with a second pattern detector, repeating patterns of a second length in the plurality of consecutive samples of the output of the FRO;

in the event at least one repeating pattern is found, counting a number of consecutive sampling instances in which a repeating pattern is found;

detecting when the count of the number of consecutive sampling instances in which a repeating pattern is found reaches a preselected threshold number;

in response to the preselected threshold number being reached, outputting an FRO lock indication signal based thereon; and

adjusting the FRO in response to the FRO lock indication signal.

12. The method of claim 11, further comprising resetting the count of the number of consecutive sampling instances in which a repeating pattern is found to zero in the event repeating patterns are not found.

13. The method of claim 11, further comprising generating an alarm when the count of the number of consecutive sampling instances in which a repeating pattern is found reaches the threshold number.

14. The method of claim 11, further comprising adjusting the FRO by one of restarting the FRO, shutting down the FRO, and changing an operating frequency of the FRO.

15. The method of claim 11, further comprising modifying a sensitivity of the detector by changing the preselected threshold number.

16. The method of claim 11, wherein an operating frequency of the FRO is greater than or equal to the sampling frequency.