A giant, configurable ring oscillator with up to 3853 stages. To enable the ring oscillator, connect one of the output pins to the first input pin (ring_in / ui_in[0]). Each output pin is connected at a different point in the ring oscillator chain, making it possible to create rings of different lengths:
| Pin | Chain length |
|---|---|
| uo[0] | 1 |
| uo[1] | 3 |
| uo[2] | 5 |
| uo[3] | 7 |
| uo[4] | 11 |
| uo[5] | 21 |
| uo[6] | 51 |
| uo[7] | 101 |
| uio[0] | 201 |
| uio[1] | 501 |
| uio[2] | 1001 |
| uio[3] | 2001 |
| uio[4] | 3001 |
| uio[5] | 3853 |
There is also an option to connect the ring oscillator internally, by driving internal_loopback high. This will create a ring oscillator with 3853 stages.
Connect one of the output pins (e.g. uio_out[5]) to ring_in or set internal_loopback to 1, and measure the output frequency.
A scope / logic analyzer to measure the output frequency and the delay between different points in the inverter chain.