A circuit separately measures a selected one of the rising-edge and falling-edge signal propagation delays through one or more circuits of interest. A number of synchronous components are configured in a loop so that they together form a free-running ring oscillator. Each synchronous component clocks a subsequent synchronous component in the ring; the subsequent synchronous component responds by clocking a later component in the ring and by clearing a previous component to prepare it for a subsequent clock. The oscillator thus produces an oscillating test signal in which the period is proportional to the clock-to-out delays of synchronous components. This proportionality provides an effective means for measuring the clock-to-out delays of those components. Other embodiments include additional asynchronous test circuit paths for which the associated signal propagation delays are of interest.