data:measure-freq d signal args
| d | data object |
| signal | signal to measure |
| level | signal crossing point (usually VDD/2) |
| args | OPTIONS |
| returns frequency in MHz using last 3 periods |
| if there aren't at least 3 periods, returns 0 |
set freq [d measure-freq VCLK -level [expr $Vdd/2.0]]