Improving Glitch Precision

If you’re using a target with its own clock source, it’s possible to set up the glitch module to have a higher resolution. The steps to do this are:

• Set the CLKGEN input source to EXTCLK.

• Set up the multiply and divide values to make CLKGEN faster than the external clock (for example, Multiply = 10 and Divide = 1). Keep in mind that extremely high clock speeds won’t work.

• Set the glitch module’s clock source to CLKGEN.

Now, one period of the glitch module’s output will be a fraction of the target’s clock period.

This overclocked glitch module is best used with the Enable Only output mode, which generates a single pulse that can last for many clock cycles. The Ext Trigger Offset and Repeat values are in terms of the glitch module’s clock, so the pulse’s start and end times can be tuned by fractions of a target period.

If the target is using an internal clock source, you can use the ChipWhisperer’s internal CLKGEN in a similar way. Though the glitch won’t be synchronous with the target’s clock, you can still insert extremely precise glitches with this method.