AN: Capstone Dive Computer Example - Quantum Leaps

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Application Note: Capstone Dive Computer Example www.state-machine.com RTC steps into shorter ones (e.g., by using the “Reminder” state pattern described in Chapter 5 of PSiCC2). 2.8.2 The QK Preemptive Kernel In some cases, breaking up long RTC steps into short enough pieces might be very difficult, and consequently the task-level response of the non-preemptive “vanilla” scheduler might be too long. An example system could be a GPS receiver. Such a receiver performs a lot of floating point number crunching on a fixed-point CPU to calculate the GPS position. At the same time, the GPS receiver must track the GPS satellite signals, which involves closing control loops in sub-millisecond intervals. It turns out that it’s not easy to break up the position-fix computation into short enough RTC steps to allow reliable signal tracking. But the RTC semantics of state machine execution does not mean that a state machine has to monopolize the CPU for the duration of the RTC step. A preemptive kernel can perform a context switch in the middle of the long RTC step to allow a higher-priority active object to run. As long as the active objects don’t share resources they can run concurrently and complete their RTC steps independently. QP includes a tiny, fully preemptive, priority-based real-time kernel called QK, which is specifically designed for processing events in the RTC fashion. Configuring QP to use the preemptive QK kernel is very easy, but you must be very careful with any resources shared among active objects. The Capstone example has been purposely designed to avoid any resource sharing among active objects, so the application code does not need to change at all to run on top of the QK, or any other preemptive kernel or RTOS for that matter. The Example1b accompanying this Application Note demonstrates the use of the preemptive QK kernel. 2.8.3 Traditional OS/RTOS QP can also work with a traditional operating system (OS), such as Windows or Linux, or virtually any real-time operating system (RTOS) such as µC/OS-II to take advantage of the existing device drivers, communication stacks, and other middleware. QP contains a portability layer, which makes adapting QP to virtually any operating system easy. The carefully designed QP portability layer allows tight integration with the underlying OS/RTOS by reusing any provided facilities for interrupt management, message queues, and memory partitions as QP critical section, event queues, or event pools, respectively. Porting QP is described in Chapter 8 of PSiCC2. Copyright © Quantum Leaps, LLC. All Rights Reserved. 22 of 29
Application Note: Capstone Dive Computer Example www.state-machine.com 3 The Quantum Spy (QS) Instrumentation The Capstone examples (Example1a and Example2b) demonstrate how to use the Quantum Spy (QS) to generate real-time trace of a running QP application. Normally, the QS instrumentation is inactive and does not add any overhead to your application, but you can turn the instrumentation on by defining the Q_SPY macro and recompiling the code. Quantum Spy (QS) is a software tracing facility built into all QP components and also available to the Application code. QS allows you to gain unprecedented visibility into your application by selectively logging almost all interesting events occurring within state machines, the framework, the kernel, and your application code. QS software tracing is minimally intrusive, offers precise timestamping, sophisticated runtime filtering of events, and good data compression (see Chapter 11 in PSiCC2 [PSiCC2]). QS can be configured to send the real-time data out of the serial port of the target device. On the STR912F MCU, QS uses the built-in USART0 to send the trace data out (see Figure 3), so the QSPY host application can conveniently receive the trace data on the host PC. The complete implementation of the QS software-tracing output consists of several steps, which are all summarized in Listing 5 (file bsp.c). (1) #ifdef Q_SPY (2) static uint32_t l_currTime32; (3) static uint16_t l_prevTime16; (4) enum AppRecords { PHILO_STAT = QS_USER /* application-specific trace records */ }; #endif /*--------------------------------------------------------------------------*/ #ifdef Q_SPY (5) uint8_t QS_onStartup(void const *arg) { (6) static uint8_t qsBuf[BSP_QS_BUF_SIZE]; /* buffer for Quantum Spy */ GPIO_InitTypeDef GPIO_InitStruct; UART_InitTypeDef UART_InitStruct; (7) QS_initBuf(qsBuf, sizeof(qsBuf)); /* configure the UART0 for QSPY output ... */ (8) SCU_APBPeriphClockConfig(__UART0, ENABLE); /* enable clock for UART0 */ (9) SCU_APBPeriphClockConfig(__GPIO3, ENABLE); /* enable clock for GPIO3 */ (10) SCU_APBPeriphReset(__UART0, DISABLE); /* remove UART0 from reset */ (11) SCU_APBPeriphReset(__GPIO3, DISABLE); /* remove GPIO3 from reset */ /* configure UART0_TX pin GPIO3.4 ... */ (12) GPIO_DeInit(GPIO3); GPIO_InitStruct.GPIO_Pin = GPIO_Pin_4; GPIO_InitStruct.GPIO_Direction = GPIO_PinOutput; GPIO_InitStruct.GPIO_Type = GPIO_Type_PushPull; GPIO_InitStruct.GPIO_IPConnected = GPIO_IPConnected_Disable; GPIO_InitStruct.GPIO_Alternate = GPIO_OutputAlt3; GPIO_Init(GPIO3, &GPIO_InitStruct); /* configure UART0... */ (13) UART_DeInit(UART0); /* force UART0 registers to reset values */ UART_InitStruct.UART_WordLength = UART_WordLength_8D; UART_InitStruct.UART_StopBits UART_InitStruct.UART_Parity = UART_StopBits_1; = UART_Parity_No; UART_InitStruct.UART_BaudRate = BSP_QS_BAUD_RATE; Copyright © Quantum Leaps, LLC. All Rights Reserved. 23 of 29
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