QP framework

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This tutorial describes how to use the QP framework with ERIKA Enterprise to develop real-time embedded applications.

QP (Quantum Platform) is a family of software frameworks that can be utilized to develop embedded applications based on the event-driven active objects programming model. QP supports manual coding of active objects through UML state machines in C (programming language) or C++ as well as fully automatic code generation by means of the graphical modeling tool QM.

ERIKA Enterprise is an open-source OSEK/ VDX Real Time Operating System (RTOS). ERIKA supports single and multi-processor platforms and provides hard real-time computing through a set of schedulers and resource management mechanisms.


We presume that the reader is familiar with ERIKA Enterprise and RT-Druid and these tools are already installed and working in his/her machine. The application examples described below have been developed for the following hardware platform: STM32F4xx (Cortex M4) architecture and the STM32F407 Discovery Board. Further information regarding the support of ERIKA for this platform can be retrieved at this link: http://erika.tuxfamily.org/wiki/index.php?title=ARM_Cortex_MX. It is also assumed that the reader has already installed the tools needed to compile and run the demo applications, as explained in the following tutorial: STM32-Integrated Debugging in Eclipse using GNU toolchain. Note that, to get ready to work with ERIKA a virtual machine with all the necessary tools already installed is available at this link: http://www.erika-enterprise.com/#VM.

Porting to ERIKA Enterprise

The porting has been developed following the indications contained in the Samek's book: Practical UML Statecharts in C/C++, Second Edition: Event-Driven Programming for Embedded Systems.

The source files of the QP framework are located in the contrib directory inside the ERIKA source tree. Currently, the supported version of the framework is the 5.2.1: http://svn.tuxfamily.org/viewvc.cgi/erika_erikae/repos/ee/trunk/ee/contrib/qpc_v521/. The source files mainly involved in the porting are qf_ports.c, located in http://svn.tuxfamily.org/viewvc.cgi/erika_erikae/repos/ee/trunk/ee/contrib/qpc_v521/src/ports/erika/, and qf_ports.h located in http://svn.tuxfamily.org/viewvc.cgi/erika_erikae/repos/ee/trunk/ee/contrib/qpc_v521/inc/ports/erika/.

The main technical choices taken during the development of the porting, along with possible alternative solutions, are summarized in the following.

  • Each active object runs in a separate ERIKA task.
  • The native type QEQueue is used to implement the event queue for active objects. QEQueue is provided by the QP framework. An alternative solution could be to use the communication mechanisms provided by the OSEK COM layer available with ERIKA.
  • Critical sections are protected by unconditionally disabling and enabling the processor interrupts through the following ERIKA routines: DisableAllInterrupts() and EnableAllInterrupts(). An alternative solution could be to use the Resource mechanism provided by ERIKA. Resources are binary semaphores handled by the Immediate Priority Ceiling protocol.
  • The blocking mechanism for event queues is implemented through an Event variable. Events is a technique provided by ERIKA to implement synchronization mechanisms.

Demo applications

A set of demo examples, derived from those already available in the QP framework, have been developed to show how to create applications with ERIKA and QP. These demos can be found in the examples folder in the ERIKA repository: http://svn.tuxfamily.org/viewvc.cgi/erika_erikae/repos/ee/trunk/ee/examples/cortex_mx/STM32F4xx/. The sub-folders containing the demos are: STM32_qpc_blinky, STM32_qpc_dpp, STM32_qpc_lcd and STM32_qpc_dpp_usart.

The demo contained in STM32_qpc_blinky implements a state machine that blinks the leds on the STM32F407 Discovery board. The demo in STM32_qpc_dpp implements the Dining Philosophers Problem (DPP) example using six concurrent active objects. The behavior of each object is implemented through a state machine. The demo can be paused and resumed by pressing the user button available on the STM32F407 Discovery board. The blue led of the board is turned on to indicate that a philosopher is eating and off otherwise. When the demo is paused the red led is turned on.

STM32_qpc_lcd and STM32_qpc_dpp_usart implement the same DPP example using respectively the LCD and the USART port to display information on the demo state, i.e paused or running, and the philosophers's state, i.e. eating, hungry or thinking.

The demo examples are composed by a set of source files. The following group of files are only related to the QP framework, that is, they do not depend neither on the underlying kernel nor on the hardware platform.

  • main.c contains the instructions to create active objects and to set and start the QP framework and its data structures, e.g. active object event queues and pools.
  • One or more source files that encode the active objects behaviour. For instance, the behaviour of the active objects of the DPP demo is defined in a couple of source files: philo.c and table.c

Other than the files listed above, which are independent both from the kernel and from the hardware, each demo contains two or more files whose code depends both on the kernel and on the hardware platform:

  • conf.oil is used to configure ERIKA objects, such as tasks, resources, alarms etc.. The configuration is specified in OIL (OSEK Implementation Language) language.
  • bsp.c contains the source code concerning the hardware platform, interrupt service routines (ISRs), ERIKA tasks and the functions of the QP framework that must be defined by the application developer.

For instance, in the DPP example the conf.oil file is structured as follows. The first part below defines:

  • (6, 7) the CPU model: Cortex M4;
  • (8), (9), (10), (11) the list of application source files;
  • (14) the compiler (GNU, i.e. gcc);
  • (16), (17), (18), (19), (20) the use of the multi-stack support with the definition of the size of the stack for ISRs (Interrupt Service Routines);
  • (23) the use of the system tick;
  • (25), (26), (27) the microcontroller model: STM32F4xx.
/*Uncomment the following EE_OPTs when using KEIL*/
(7)    MODEL = M4;
(8)    APP_SRC = "main.c";
(9)    APP_SRC = "bsp.c";
(10)    APP_SRC = "philo.c";
(11)    APP_SRC = "table.c";
(16)    MULTI_STACK = TRUE {
(17)        IRQ_STACK = TRUE {
(18)            SYS_SIZE=512;
(19)        };
(20)    };
(21) };
(23) EE_OPT = "__USE_SYSTICK__";
(25) MCU_DATA = STM32 {
(26)     MODEL = STM32F4xx;
(27) };

The following lines of code define:

  • (3), (4) the use of the QP framework (version 5.2.1);
  • from (6) to (22) the use of the drivers that handle some of the microcontroller's peripherals (e.g GPIO) and some of the board's devices (buttons and leds);
  • from (25) to (35) some configurations for the kernel. In particular, at line (35), the attribute KERNEL_TYPE is set to ECC2. Since application tasks must use an Event variable when the application is developed using the QP framework, kernel type ECC2 is a mandatory setting, see below for further details.
(1) EE_OPT = "__ADD_LIBS__";
(3) LIB = ENABLE { NAME = "QPC_V521"; };
(4) EE_OPT = "__LIB_QPC_V521__";
(6) LIB = ENABLE { NAME = "ST_CMSIS"; };
(9)     STM32F4XX_SPD = ENABLE {
(10)        USEGPIO = TRUE;
(11)         USEEXTI = TRUE;
(12)         USESYSCFG = TRUE; 
(13)         USEMISC = TRUE;
(14)         };
(15)     };
(19)     USELEDS = TRUE;
(21)     };
(22) };

The following configuration code, from line 1 to line 65, defines the application tasks. Note that, each task defines its private stack, all tasks are activated at the system start up (AUTOSTART = TRUE), namely after that the StartOS() function is called, which in turn is called by QF_run(), see file qf_port.c. The code at line 67 defines the Event variable QFEvent, which is used for the blocking mechanism of QP event queues. The code from line 69 to line 73 enables the system tick interrupt and defines the related ISR.

(1) TASK Philo0Task {
(2)     PRIORITY = 0x01;
(3)     AUTOSTART = TRUE; { /* NOTE: AUTOSTART should be always TRUE*/}
(4)    STACK = PRIVATE {
(5)     SYS_SIZE = 512;
(6)     };
(7)     ACTIVATION = 1;    /* only one pending activation */
(8)     SCHEDULE = FULL;
(9)     EVENT = QFEvent;
(10) };
(12) TASK Philo1Task {
(13)     PRIORITY = 0x02;
(14)     AUTOSTART = TRUE;  /* NOTE: AUTOSTART should be always TRUE*/
(15)     STACK = PRIVATE {
(16)         SYS_SIZE = 512;
(17)     };
(18)     ACTIVATION = 1;    /* only one pending activation */
(19)     SCHEDULE = FULL;
(20)     EVENT = QFEvent;
(21) };
(23) TASK Philo2Task {
(24)     PRIORITY = 0x03;
(25)     AUTOSTART = TRUE;  /* NOTE: AUTOSTART should be always TRUE*/
(26)     STACK = PRIVATE {
(27)         SYS_SIZE = 512;
(28)     };
(29)     ACTIVATION = 1;    /* only one pending activation */
(30)     SCHEDULE = FULL;
(31)     EVENT = QFEvent;
(32) };
(34) TASK Philo3Task {
(35)    PRIORITY = 0x04;
(36)     AUTOSTART = TRUE;  /* NOTE: AUTOSTART should be always TRUE*/
(37)     STACK = PRIVATE {
(38)         SYS_SIZE = 512;
(39)     };
(40)     ACTIVATION = 1;    /* only one pending activation */
(41)     SCHEDULE = FULL;
(42)     EVENT = QFEvent;
(43) };
(45) TASK Philo4Task {
(46)     PRIORITY = 0x05;
(47)     AUTOSTART = TRUE;  /* NOTE: AUTOSTART should be always TRUE*/
(48)     STACK = PRIVATE {
(49)         SYS_SIZE = 512;
(50)     };
(51)     ACTIVATION = 1;    /* only one pending activation */
(52)     SCHEDULE = FULL;
(53)     EVENT = QFEvent;
(54) };
(56) TASK TableTask {
(57)     PRIORITY = 0x06;
(58)     AUTOSTART = TRUE;  /* NOTE: AUTOSTART should be always TRUE*/
(59)     STACK = PRIVATE {
(60)         SYS_SIZE = 512;
(61)     };
(62)     ACTIVATION = 1;    /* only one pending activation */
(63)     SCHEDULE = FULL;
(64)     EVENT = QFEvent;
(65) };
(67) EVENT QFEvent { MASK = AUTO; };
(69) ISR systick_handler {
(70)     CATEGORY = 2;
(71)     ENTRY = "SYSTICK";
(72)     PRIORITY = 1;
(73) };

As far as the OIL configuration file is concerned, any application developed with QP and ERIKA must observe the following rules:

  • For each QP active object a corresponding ERIKA task must be created. The task must have the priority attribute (PRIORITY) equal to the active object priority.
  • Each task must declare QFEvent through its event attribute (EVENT = QFEvent).
  • Each task must use a private stack.
  • Each task must set its AUTOSTART attribute equal to TRUE.
  • All tasks must be extended tasks, hence, KERNEL_TYPE attribute must be set to Extended Conformance Class 2 (ECC2).

It is worth noting that, it is not necessary that the name of a task corresponds to the name of the related active object. The only requirement is that for each active object it must exist at least a task with the same priority number, and the number of tasks must match the number of active objects.

For further information on how to create OIL configuration files see the RT-Druid Reference Manual.

The body of each task must be defined in one of the application source files. In the demo examples available with ERIKA the task bodies are defined in the file bsp.c. All tasks are coded using the same scheme as it follows:



Each task has to call the task_function() routine and passing as argument the element of the array pdata indexed by the task name, namely TaskName. task_function() is defined in qf_port.c and pdata is an array where each element is a data structure that defines the associated active object. Notice that, when task_function() is called it executes the code of the active object associated with task TaskName. Each task must be terminated by a call to TerminateTask(). Note that, as long as the application is running, a call to task_function() never ends. For this reason each task must have a private stack.

Other than task bodies, file bsp.c provides the following QP functions that must be defined by the application developer:

  • QF_onStartup(),
  • QF_onCleanup(),
  • Q_onAssert(),
  • QF_onIdle().

Some other functions concerning to the tracing tool QP Spy are also defined in bsp.c.

QP Modeler

QM is a graphical modeling tool for the development of embedded applications based on the QP framework. It is freeware and usable to to develop real-time embedded applications using UML state machines and ERIKA Enterprise.

We suggest the following steps be used in creating your application through QM.

  1. Design a graphical model of the application using QM.
  2. Generate the source code from the graphical model using QM.
  3. Handwrite file bsp.c with the code needed to handle the hardware, to define the QP functions that must be coded by the application developer, and to define tasks and other ERIKA related stuffs, such as ISRs. Of course, instead of just creating bsp.c the source code can be divided into more files.
  4. Handwrite the ERIKA configuration file, usually named conf.oil.

For instance, taking as an example the DPP demo, inside the folder there is a file named dpp.qm. This file contains the graphical model of the demo. By opening dpp.qm with QM it is possible both to see the graphical model and to generate the relative source code. QM generates four files: main.c, philo.c, table.c and dpp.h. Note that, these files contain the code only related to the QP framework and independent from both ERIKA and from the hardware platform. As already stated above, the source files that depend on the kernel and on the hardware, that is bsp.c and conf.oil, must be handwritten by the application developer.

Note that, to work with the version 5.2.1 of the QP framework the developer must use the version 3.0.0 of QM. Otherwise, QM can generate a source code inconsistent with the version of QP currently supported by ERIKA.

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