super-simple, run-to-completion, single-stack kernel that perfectly matches the
universally assumed run-to-completion semantics required for state machine execution.
Testing Support
A running application built of concurrently executing state machines is a highly
structured affair where all important system interactions funnel through the event-
driven framework that ties all the state machines together. By instrumenting just this
tiny “funnel” code, you can gain unprecedented insight into the live system. In fact, the
software trace data from an instrumented event-driven framework can tell you much
more about the application than any traditional real-time operating system (RTOS)
because the framework “knows” so much more about the application.
Chapter 11 describes the new QS (“spy”) component that provides a comprehensive
software-tracing instrumentation to the QP event-driven platform. The trace data
produced by the QS component allows you to perform a live analysis of your running
real-time embedded system with minimal target system resources and without stopping
or significantly slowing down the code. Among other things, you can reconstruct
complete sequence diagrams and detailed, timestamped state machine activities for all
active objects in the system. You can monitor all event exchanges, event queues,
event pools, time events (timers), and preemptions and context switches. You can also
use QS to add your own instrumentation to the application-level code.
Ultra-Lightweight QP-nano Version
The event-driven approach with state machines scales down better than any
conventional real-time kernel or RTOS. To address really small embedded systems, a
reduced QP version called QP-nano implements a subset of features supported in QP/C
or QP/C++. QP-nano has been specifically designed to enable event-driven
programming with hierarchical state machines on low-end 8- and 16-bit
microcontrollers (MCUs), such as AVR, MSP430, 8051, PICmicro, 68HC(S)08, M16C,
and many others. Typically, QP-nano requires around 1-2KB of ROM and just a few
bytes of RAM per state machine. I describe QP-nano in Chapter 12.
Removed Quantum Metaphor
In the first edition of PSiCC, I proposed a quantum-mechanical metaphor as a way of
thinking about the event-driven software systems. Though I still believe that this
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xx Preface
