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 ?