The reference platform

The preferred design strategy for embedded CPU cores is reduced instruction set computer (RISC). Among all the RISC CPU architectures, a number of reference designs are used as guidelines by silicon manufacturers to produce the core logic to integrate into the microcontroller. Each reference design differs from the others in a number of characteristics of the CPU implementation. Each reference design includes one or more families of microprocessors integrated in embedded systems, sharing the following characteristics:

• Word size used for registers and addresses (8-bit, 16-bit, 32-bit, or 64-bit)
• Instruction set
• Register configurations
• Endianness

• Extended CPU features (interrupt controller, FPU, MMU)
• Caching strategies
• Pipeline design

Choosing a reference platform for your embedded system depends on your project needs. Smaller, less feature-rich processors are generally more suited to low energy consumption, have a smaller MCU packaging, and are less expensive. Higher-end systems, on the other hand, come with a bigger set of resources and some of them have dedicated hardware to cope with challenging calculations (such as a floating point unit, or an Advanced Encryption Standard (AES) hardware module to offload symmetric encryption operations). 8-bit and 16-bit core designs are slowly giving way to 32-bit architectures, but some successful designs remain relatively popular in some niche markets and among hobbyists.