nxtOSEK: Rate Monotonic Scheduling

Rate Monotonic Scheduling

While developing a high speed real-time control application on the NXT, you may encounter some difficulty to design the application which responses against external stimulations within expected deadline. (I.e. if you wanted to design a real fast Line Tracing Robot,
you would need to consider a lot of things, especially about real-time control for line detection, robot position control…).
nxtOSEK provides OSEK Alarm based Rate Monotonic Scheduling to execute a NXT application on real-time multi rate/multi tasking environment. This technology is basically same as industrial real-time control systems especially in automotive.
There are several key points to design Rate Monotonic Scheduling by using nxtOSEK:

Shortest Task execution period is 1msec and all Task execution periods are integral multiplication of 1msec
Tasks with shorter periods/deadlines are given higher priorities (greater value means higher priority)
All periodical Tasks are executed by the OSEK Alarm Counter
All periodical Tasks have same ALARMTIME
(Shared global resources are protected by GetResource and ReleaseResource)

In rms.c and rms.oil, three periodical execution Tasks are defined and Tasks have the following specifications. Task1 and Task2 control Servo Motor A and B independently and if the Touch Sensor was touched, the Motors would be stopped.

Task1: period = 1msec, Priority = 3, ALARMTIME = 1
Task2: period = 500msec, Priority = 2, ALARMTIME = 1
TaskLCD: period = 500msec , Priority = 1, ALARMTIME = 1

To test this Rate Monotonic Scheduling example on the NXT, you need to have the following NXT devices:

2 Servo Motors on Port A and Port B
1 Touch Sensor on Port S1

samples\rms\rms.c

/* rms.c */
#include "kernel.h"
#include "kernel_id.h"
#include "ecrobot_interface.h"

/* OSEK declarations */
DeclareCounter(SysTimerCnt);
DeclareTask(Task1);
DeclareTask(Task2);
DeclareTask(TaskLCD);

/* nxtOSEK hooks */
void ecrobot_device_initialize(void)
{
nxt_motor_set_speed(NXT_PORT_A, 0, 1);
nxt_motor_set_speed(NXT_PORT_B, 0, 1);
}

void ecrobot_device_terminate(void)
{
nxt_motor_set_speed(NXT_PORT_A, 0, 1);
nxt_motor_set_speed(NXT_PORT_B, 0, 1);
}

/* nxtOSEK hook to be invoked from an ISR in category 2 */
void user_1ms_isr_type2(void)
{
  StatusType ercd;

  ercd = SignalCounter(SysTimerCnt); /* Increment OSEK Alarm Counter */
  if (ercd != E_OK)
{
    ShutdownOS(ercd);
  }
}

/* Task1 executed every 1msec */
TASK(Task1)
{
  if (ecrobot_get_touch_sensor(NXT_PORT_S1))
{
   nxt_motor_set_speed(NXT_PORT_A, 0, 1);
  }
  else
  {
   nxt_motor_set_speed(NXT_PORT_A, 50, 1);
  }

  TerminateTask();
}

/* Task2 executed every 500msec */
TASK(Task2)
{
  if (ecrobot_get_touch_sensor(NXT_PORT_S1))
{
   nxt_motor_set_speed(NXT_PORT_B, 0, 1);
  }
  else
  {
   nxt_motor_set_speed(NXT_PORT_B, 50, 1);
  }

  TerminateTask();
}

/* TaskLCD executed every 500msec */
TASK(TaskLCD)
{
  ecrobot_status_monitor("RMS");

  TerminateTask();
}

samples\rms\rms.oil

#include "implementation.oil"

CPU ATMEL_AT91SAM7S256
{
  OS LEJOS_OSEK
  {
    STATUS = EXTENDED;
    STARTUPHOOK = FALSE;
    ERRORHOOK = FALSE;
    SHUTDOWNHOOK = FALSE;
    PRETASKHOOK = FALSE;
    POSTTASKHOOK = FALSE;
    USEGETSERVICEID = FALSE;
    USEPARAMETERACCESS = FALSE;
    USERESSCHEDULER = FALSE;
  };

  /* Definition of application mode */
  APPMODE appmode1{};

  /* Definition of Task1 */
  TASK Task1
  {
    AUTOSTART = FALSE;
    PRIORITY = 3;
    ACTIVATION = 1;
    SCHEDULE = FULL;
    STACKSIZE = 512; /* Stack size */
  };

  /* Definition of Task2 */
  TASK Task2
  {
    AUTOSTART = FALSE;
    PRIORITY = 2;
    ACTIVATION = 1;
    SCHEDULE = FULL;
    STACKSIZE = 512; /* Stack size */
  };

  /* Definition of TaskLCD */
  TASK TaskLCD
  {
    AUTOSTART = FALSE;
    PRIORITY = 1;
    ACTIVATION = 1;
    SCHEDULE = FULL;
    STACKSIZE = 512; /* Stack size */
  };

  /* Definition of OSEK Alarm Counter */
  COUNTER SysTimerCnt
  {
    MINCYCLE = 1;
    MAXALLOWEDVALUE = 10000;
    TICKSPERBASE = 1; /* One tick is equal to 1msec */
  };

  /* Definition of Task1 execution timing */
  ALARM cyclic_alarm1
  {
    COUNTER = SysTimerCnt;
    ACTION = ACTIVATETASK
    {
      TASK = Task1;
    };
    AUTOSTART = TRUE
    {
      ALARMTIME = 1;
      CYCLETIME = 1; /* Task1 is executed every 1msec */
      APPMODE = appmode1;
    };
  };

  /* Definition of Task2 execution timing */
  ALARM cyclic_alarm2
  {
    COUNTER = SysTimerCnt;
    ACTION = ACTIVATETASK
    {
      TASK = Task2;
    };
    AUTOSTART = TRUE
    {
      ALARMTIME = 1;
      CYCLETIME = 500; /* Task2 is executed every 500msec */
      APPMODE = appmode1;
    };
  };

  /* Definition of TaskLCD execution timing */
  ALARM cyclic_alarmLCD
  {
    COUNTER = SysTimerCnt;
    ACTION = ACTIVATETASK
    {
      TASK = TaskLCD;
    };
    AUTOSTART = TRUE
    {
      ALARMTIME = 1;
      CYCLETIME = 500; /* TaskLCD is executed every 500msec */
      APPMODE = appmode1;
    };
  };
};

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