Method for configuring clock ratios in a microprocessor

Abstract

Disclosed is a method and apparatus for software configuration of a processor clock ratio. Boot code that the processor executes in response to a reset event correctly configures the clock ratio to a desired value, where the desired value can be set via a user interface. The processor then checks the clock ratio against a desired clock ratio value stored in a nonvolatile memory. If the clock ratio is the same as the desired clock ratio value, then the processor completes the boot of the processor. If the clock ratio is different from the desired value, then the processor writes the desired value into a latch connected to the on clock configuration input terminals of the processor and inhibits reset of the latch. The processor then generates another reset event. In this reset cycle, the processor will sense the desired clock ratio value driven onto the clock configuration input terminals by the latch and boot with the desired clock ratio.