The BA20 is a small, ultra-low-power, and very efficient 32-bit processor. It is an excellent step up from the 8051 and other 8- and 16-bit microcontrollers, and ideal for energy-sensitive deeply embedded applications such as wearable electronics, Internet of Things (IoT) sensors, wireless communication, and other mixed-signal ICs. Thanks to its PipelineZero? architecture, the BA20 core delivers a surprisingly high processing efficiency with a tiny silicon footprint. True single-cycle instruction execution of the BA2 ISA, zero-delay branches, no pipeline-stalling overheads, and an optional hardware multiply unit enable the BA20 to operate with efficiency as high as 3.48 CoreMarks/MHz. With no pipeline stages in the instruction execution path, the BA20 uses a minimal number of flip-flops and a simplified CPU control, so its processing efficiency comes without a silicon area penalty. These advantages plus advanced power management features and the extreme code density of the BA2? instruction set, make the BA20 the most energy-efficient 32-bit processor currently available. The BA20's capabilities can be enhanced with options including a single-precision floating-point unit, a multiply-accumulate unit, and a unit accelerating the DSP extensions of the BA2 instruction set. Interrupt response time can be optimized further with a vectored interrupt controller, and an optional memory protection unit can be used to protect application code and/or data from corruption. The core's system interface uses two AMBA? AXI4? or optionally two AHB-Lite? buses, one for data and one for instructions. Two tightly-coupled embedded memory (EMEM) buses allow fast access for time-critical code and data, and can be used for inter-core communication in a multi-core architecture. The BA20 supports the variable instruction length BA2 instruction set, benefits from its extreme code density, and is binary compatible with other members of the BA2x processor family. Programming is facilitated with the included C/C++ tool chain, Eclipse IDE, architectural simulator, and ported C libraries. Advanced debugging capabilities, and off-the-shelf development boards can further ease software development. Additional peripherals and bus infrastructure cores or complete subsystems can be ordered with the processor core to simplify SoC integration. Part of the royalty-free BA2x family, the BA20 processor core has been designed for easy reuse and integration, has been rigorously verified, and is production proven.