Is it possible to disable the VCC-INT decoupling caps on the CW305?

Hi, I have some problems with voltage glitching.

  1. After the trigger, the voltage glitch is not generated immediately but after several clock periods.

  2. I adjusted scope.glitch.ext_offset and scope.glitch.repeat, but the attack was still unsuccessful.

I set Input Clock Source to ChipWhisperer HS-IO, and other settings are as follows:

target.pll.pll_outenable_set(False, 0)
target.pll.pll_outenable_set(True, 1)
target.pll.pll_outenable_set(False, 2)

# run PLL1 at 100 MHz:
target.pll.pll_outfreq_set(10E6, 1)

# 1ms is plenty of idling time
target.clkusbautooff = True
target.clksleeptime = 1

scope.clock.clkgen_freq = 10E6
scope.glitch.clk_src = "clkgen" 
scope.glitch.output = "enable_only"
scope.glitch.trigger_src = "ext_continuous" = True  

scope.glitch.ext_offset = 1
scope.glitch.repeat = 5

The blue wave is clock signal, the green one is voltage, the yellow one is trigger signal.

Regarding the second problem above, I think it may be because there is filtering behind the SMA connector X3, so the voltage glitch will not affect the target FPGA. Is it possible to disable the VCC-INT decoupling capacitor on the CW305? Or I’m wrong, there are other reasons I don’t know.

Thank you.

The CW305 can be ordered with or without VCC-INT decoupling capacitors. Typically they are not mounted, to get better power traces (and possibly for better results with voltage glitching, although here you have to be mindful of the possibility of corrupting the FPGA itself).

The optionally mounted capacitors are C87-C92: CW305 Artix FPGA Target - NewAE Hardware Product Documentation
Can you confirm that they are indeed mounted on your CW305?

Yes, I think the VCC-INT decoupling capacitors are indeed installed on my CW305.

Does that mean they cannot be disabled or removed unless ordered without decoupling capacitors?

Thank you for your help.

There is no way to disable them other than desoldering them.
There are pros and cons to having or not having the decoupling capacitors; it’s explained here (search for VCC-INT).

I see. Thank you so much.