The decision regarding the best suitable microprocessor for a given task is one of the most challenging assignments a hardware designer has to face.
In this paper, we make a comparison of cycle-accurate VHDL clones of the 8-bit Atmel ATmega, the 16-bit Texas Instruments MSP430, and the 32-bit ARM Cortex-M0+. We investigate their runtime, chip area, power, and energy characteristics regarding Elliptic Curve Cryptography (ECC), one of the practically most resource-critical public-key cryptography systems. If ECC is not implemented with greatest care, its implementation can lead to excruciating runtimes or enable practical side-channel attacks. Considering those important requirements, we present a constant runtime, side-channel protected, and resource saving scalar multiplication algorithm. To tap the full potential of all three microprocessors, we perform assembly optimizations and add carefully crafted instruction-set extensions. To the best of our knowledge, this is the first thorough software and hardware comparison of these three embedded microprocessors.