Snoop detection on calibrated bus
View Patent ↗An electronic system having a high speed signaling bus requiring training (calibration) of a calibrated item in a driver circuitry or a receiver circuitry for reliable operation. At manufacturing or in a secure location, secure calibration coefficients are determined for the electronic system and are stored in a non-volatile storage. During operation, the high speed signaling bus may be re-calibrated, resulting in a new currently active calibration coefficient for the calibrated item. A coefficient watchdog checks a new coefficient value selected by the re-calibration at present environmental conditions such as voltage and temperature against the secure calibration coefficients. If the new calibration coefficient value is the same as a calibration coefficient value in an acceptably close secure calibration coefficient, the new calibration coefficient is accepted; if not, a potentially probed warning is created by the coefficient watchdog.
1. A method of determining that a high speed signaling bus in an electronic system has been probed, comprising:
in a secure environment, determining secure calibration coefficients, at specific environmental conditions, for a calibrated item associated with the high speed signaling bus;
in the secure environment, storing the secure calibration coefficients in a non-volatile storage;
providing a coefficient watchdog in the electronic system, the coefficient watchdog, when the electronic system is operating and re-calibrates the calibrated item, determining if a new calibration coefficient resulting from the re-calibration is acceptable; if not acceptable, asserting, by the coefficient watchdog, a potentially probed high speed signaling bus condition.
2. The method of claim 1 , the specific environmental conditions including at least one of voltage and temperature.
3. The method of claim 1 , the non-volatile storage being an electrically programmable fuse (eFuse).
4. The method of claim 1 further comprising:
performing the re-calibration when a bit error rate (BER) increases to a prespecified value.
5. The method of claim 1 further comprising:
performing the re-calibration when the electronic system is re-booted.
6. The method of claim 1 further comprising;
performing the re-calibration at prespecified intervals.
7. The method of claim 1 further comprising:
the coefficient watchdog determining if the new calibration coefficient is acceptable comprises:
finding a value in the secure calibration coefficients that equals a value of the new calibration coefficient;
determining if a nearest determined calibration point having the value of the new calibration point is too far away, given current environmental conditions;
if the nearest determined calibration point having the value of the new calibration coefficient point is not too far away, then accepting the new calibration coefficient; and
if the nearest secure calibration coefficient point having the value of the new calibration coefficient point is too far away, then asserting the potentially probed high speed signaling bus condition.
8. The method of claim 7 wherein determining if the nearest determined calibration point having the value of the new calibration point is too far away uses a bounding box.
9. The method of claim 7 wherein determining if the nearest determined calibration point having the value of the new calibration point is too far away uses a secure calibration vector.
10. The method of claim 1 , wherein the calibrated item is a phase rotator.
11. The method of claim 1 , wherein the calibrated item is a terminator.
12. The method of claim 1 , wherein the calibrated item is a driver impedance.
13. The method of claim 1 , wherein the calibrated item is a pre-emphasis driver.
14. An electronic system comprising:
a high speed signaling bus having a calibrated item to optimize signal transmission on the high speed signaling bus;
a secure calibration coefficients non-volatile storage to hold calibration coefficients determined at a secure location;
a control circuitry to re-calibrate the calibrated item and determine a new currently active calibration coefficient for the calibrated item;
a coefficient watchdog having access to the secure calibration coefficients, the new currently active calibration coefficient, and at least one environmental condition, the coefficient watchdog configured to output a potentially probed high speed signaling bus if the new currently active calibration coefficient is unacceptable for the at least one environmental condition.
15. The electronic system of claim 14 , the non-volatile storage being an electrically programmable fuse (eFuse).
16. The electronic system of claim 14 , the calibrated item being a phase rotator.
17. The electronic system of claim 14 , the calibrated item being a driver impedance.
18. The electronic system of claim 14 , the calibrated item being a terminator.
19. The electronic system of claim 14 , the calibrated item being a pre-emphasis driver.
20. The electronic system of claim 14 , the control circuitry configured to re-calibrate the calibrated item at bring up of the electronic system.
21. The electronic system of claim 14 , the control circuitry configured to re-calibrate the calibrated item when a bit error rate on the high speed signaling bus exceeds a predetermined value.
22. The electronic system of claim 14 , the control circuitry configured to re-calibrate the calibrated item at prespecified intervals.
23. The electronic system of claim 14 , the coefficient watchdog configured to determine acceptability of the new calibration coefficient by comparing a value of the new calibration coefficient against values at secure calibration coefficient points and rating the new currently active calibration coefficient unacceptable based on a secure calibration vector, the secure calibration vector being a mathematical distance from the new calibration coefficient point selected based on a value and one or more secure calibration coefficient points.