Its a shame no one makes a cheap board with the XC9536XL on it, as for most people is not practical to solder SMD
What does the part of the circuit with 3 inverters in series do ?
There is an XC9572XL board for $15
https://www.seeedstudio.com/XC9572XL-CP ... p-799.html
and CoolRunner too
https://www.seeedstudio.com/XC2C64A-Coo ... p-800.html
The ring oscillator - in that design you can switch between local oscillator - the ring one, and the external oscillator. As the ring one does around 150MHz, you can measure periods with 6ns resolution. There are a few config options, so you can first measure the ring freq against millis() for example - like calibration. And then you may use calibrated ring oscillator for other measurements.
So the talented people may play. It was meant a toy for talented arduinists interested. Based on above seeed's 9572 board.
For experiments and study I recommend at least the 72 as it is bigger and you can place a lot of stuff inside.
36 is good when you have something ready - like the tft interface for example. But it is an additional level of effort most duinists avoid
PS: for $30 you can get a board with Spartan6 FPGA. So, indeed, the above CPLD boards shall cost something like $0.002 then
As a pure breakout board without buttons, leds and regulator: 9536=$1, capacitors=$0.20, board from itead=$1.50, all single quantity (excep itead) - that is all