Patent ID: 8341451
Filing Date: 2012-12-25
Classification: G06F

Abstract:
1. A circuit for determining the frequency of a first oscillating reference signal generated by a first independently-oscillating reference oscillator, the circuit comprising: a boot memory storing boot code comprising clock configuration code; and a real-time clock for measuring time in seconds, the real-time clock comprising a second independently-oscillating reference oscillator arranged to generate a second oscillating reference signal having a known frequency, and the real-time clock being arranged to use the frequency of the second reference signal as a reference, the frequency of the second reference signal being 2 a processor coupled to the boot memory and the second reference oscillator, arranged to execute the boot code from the boot memory upon booting, wherein when executed the clock configuration code operates the processor to discover the frequency of the first reference signal by reference to the second reference signal; wherein the frequency of the first reference signal is one of a predetermined set of quantised values spaced more widely than an initially known accuracy of the frequency of the second reference signal, and the clock configuration code discovers the frequency of the first reference signal by reference to the set of quantised values; and wherein the circuit further comprises calibration means arranged, after the frequency of the first reference signal has been discovered, to calibrate the real-time clock by determining the frequency of the second reference signal to a greater accuracy than initially known by reference to the discovered frequency of the first reference signal.