This is a 9-stage Current Starved Ring Oscillator. The higher the number of stages, the lower the frequency. Ring Oscillators are chains of inverters (each inverter is a "stage"), usually an odd number 3 or higher. Ideally at any given time one of the stages is changing it's state, followed by the next one running around the loop. One way to get some frequency control is to constrain the current. Having per-stage current mirrors is the more common option for CSROs and allows the IO to swing from rail to rail. There are other configurations with different trade-offs.
Vcontrol controls the amount of current running through the current mirrors which controls the frequency (lower is slower, higher is faster).
Venable powers the circuit and is a way to turn the circuit on and off while the project is selected. High-side control does take more area than low side control would, but results in low outputs when inactive.
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