README.md


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Tamper detection for Atmel AVR ATtiny828 MCU on the Cryptech alpha
board, rev02.
   *************
   * P A N I C *
   *   button  *
   *************
    /
   /
  /
AVR ---- SPI mux ---- FPGA
            |          |
            |         ARM
           MKM


AVR -- Atmel MCU
FPGA -- FPGA
MKM -- Master Key Memory, 23K640 SRAM
SPI mux -- 2 x MC74AC244DW
ARM -- ARM CPU
The MKM holds the master key for the device.
The AVR, MKM and the mux are battery powered.
The AVR and the FPGA are sharing access to the MKM through the mux,
with the AVR connected to the pins used for deciding who's in control
of the memory. The FPGA is in control by default.
When the panic button is pressed, the AVR grabs the MKM and writes
zeros to it as quickly as possible. In idle mode, i.e. when the panic
button is not pressed, the AVR tries to consume as little power as
possible.