Sawtooth course of Single Point of Trace - ChipWhisperer LiteArm


I am trying to capture single Instructions and investigate in there Leakage with Chipwhisperer LiteARM.
Therefor I plotted one Point of each measured Powertrace that corresponds to the investigated Instruction and noticed an Sawtooth course with a Period of around 1750 Traces.

This I noticed for multiple different Instruction: xor, shift, str

Capture frq. is set to x4

Instruction Prefetch is turned of:

  • uint32_t *flash_acr = 0x40022000;
  • *flash_acr &= ~(0x10);
    Tested with Prefetch turned on/off : Makes no difference

Capture shows 6000 Traces with random Input

Capture shows 6000 Traces with fixed Input

The Direction of the Sawtooth changes when i look on some clock cycles further.

Instruction: “8000250: 60c4 str r4, [r0, #12]”

Does anyone know a reason for this effect ?

I created a new topic for this problem : CWLiteArm - Sawtooth course of Traces