In this chapter I describe a reduced version of the event-driven infrastructure called QP-nano, which has been specifically designed to enable active object computing with UML-style hierarchical state machines on low-end 8-and 16-bit single-chip microcontrollers (MCUs). By low-end MCUs I mean devices such as 8051, PIC, AVR, MSP430, 68HC08/11/12, R8C/Tiny, and others alike, with a few hundred bytes of RAM and a few kilobytes of ROM. Embedded in myriads of products, these “invisible computers” far outnumber all other processor types in a similar way as countless species of insects far outnumber all other life forms on Earth [Turely 02],

Even though the QP event-driven platform is by no means big, a minimal QP application still requires around 1KB of RAM and some 10KB of ROM (see Figure 7.2 in Chapter 7), which is comparable to the footprint of a very small, bare-bones conventional RTOS. In comparison, a minimal QP-nano application can fit in a system with just 100 bytes of RAM and 2KB of ROM. This tiny footprint, especially in RAM, makes QP-nano ideal for high-volume, cost-sensitive, event-driven applications such as motor control, lighting control, capacitive touch sensing, remote access control, RFID, thermostats, small appliances, toys, power supplies, battery chargers, or just about any custom system on a chip (SOC or ASIC) that contains a small processor inside. Also, because the event-driven paradigm naturally uses the CPU only when handling events and otherwise can very easily switch the CPU into a low-power sleep mode (see Section 6.3.7 in Chapter 6), QP-nano is particularly suitable for ultra-low power applications, such as wireless sensor networks or implantable medical devices.