systemAutomotive Embedded Systems part3(OSEK/VDX) Cont.

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Automotive Embedded
Systems part3
(OSEK/VDX) Cont.
ENG.KEROLES SHENOUDA
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OSEK/VDX
Operating System
it's time to wake up 
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Extended tasks
THE TASK THAT ARE ABLE TO WAIT FOR AN EVENT
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States of an extended task
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event
 An event is like a flag that is raised to signal something just happened.
 An event is private: It is a property of an Extended Task. Only the owning task may
wait for the event.
 It is a N producers / 1 consumer model
 Any task (extended or basic) or Interrupt Service Routines Category 2 may invoke the
service which set an event.
 One task (an only one) may get the event (ie invoke the service which wait for an event.
 An Extended Task may wait for many events simultaneously
 The first to come wakes up the task.
 an event corresponds to a binary mask: 0x01, 0x02, 0x04, ...
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Event mask
 Operation:
 Event X signaling : ev_set |= mask_X;
 Is event X arrived ? : ev_set & mask_X;
 Wait for event X : ev_wait | mask_X;
 Clear event X : ev_set &= ~mask_X;
 In practice, these operations are done in a simpler way by using the
following services.
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Events’ services
 StatusType SetEvent(TaskType <TaskID>, EventMaskType <Mask>);
 Events of task <TaskID> are set according to the <Mask> passed as 2nd argument.
 StatusType is an error code:
 E_OK: no error;
 E_OS_ID: invalid TaskId;
 E_OS_ACCESS: TaskID is not an extended task (not able to manage events);
 E_OS_STATE: Events cannot be set because the target task is in the SUSPENDED state.
 This service is not blocking and may be called from a task or an ISR2
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Events’ services
 StatusType ClearEvent(EventMaskType <Mask>);
 The events selected by <Mask> are cleared.
 should be called by the owning task (only);
 StatusType is an error code:
 E_OK: no error;
 E_OS_ACCESS: The calling task is not an extended one (so it does not mabage events);
 E_OS_CALLEVEL: The caller is not a task. non-blocking service.
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Events’ services
 StatusType GetEvent(TaskType <TaskId>, EventMaskRefType event);
 The event mask of the task <TaskId> is copied to the variable event (A pointer to
an EventMaskType is passed to the service);
 StatusType is an error code:
 E_OK: no error;
 E_OS_ID: invalid TaskID;
 E_OS_ACCESS: TaskID is nor an extended task;
 E_OS_STATE: Events may not be copied because the target task is in the
SUSPENDED state.
 Non-blocking service, my be called from a task or an ISR2
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Events’ services
 StatusType WaitEvent(EventMaskType <EventID>);
 Put the calling task in the WAITING state until one of the events is set.
 May be called by the event owning (extended) task only;
 StatusType is an error code:
 E_OK: no error;
 E_OS_ACCESS: The calling task is not an extended one;
 E_OS_RESOURCE: The task has not released all the resources (will be
explained later);
 E_OS_CALLEVEL: The caller is not a task
 Blocking service.
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Lab4: extended task based on
event
#LEARN_IN_DEPTH
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Lab4
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 Create two tasks T1 and T2
 T1 is basic task (sequential task)
 T2 is Extended task based on event
ev1
 T2 priority > T1
 The Autosatrt is enabled for both
T1 and T2
 Send a messages for Both T1 and T2 by writing on 7-segment
 See the following code and expect what happen on the Physical Board

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Let us first, write the oil file
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Lab4.oil
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See the following code and expect
what happen on the Physical Board
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Draw a Task Timeline

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Lab4.c
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#Learn In Depth 
expect what happen on the Physical Board

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Let us see the Solution
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Learn in Depth what happen
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T2 is an extended task.
During A period, T2 is
running and
T1 is ready, because
T2_priority > T1_priority

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Then T2 wait for E1 and
blocks. T1 runs (B period)
Learn in Depth what happen

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T1 will pull on the PB2
If it is pressed then will
Set the E1 (event)
Learn in Depth what happen

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Then will press the PB2
Learn in Depth what happen

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Then will press the
PB2
T2 is released and
since
P(T2) > P(T1), T2
runs (C period),
Learn in Depth what happen

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clears E1 and
continues to run
(D period).
Learn in Depth what happen

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24
Will
Conten.
Learn in Depth what happen

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Learn in Depth what happen
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Interrupts
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Interrupts
 2 kinds of interrupts (Interrupt Service Routine or ISR) are defined
in OSEK.
 Level 1 interrupts
 are very fast;
 depends on the hardware capabilities of the micro-controller;
 are not allowed to do a system call;
 usually difficult to port to another micro-controller;
 Level 2 interrupts
 are not as fast as level 1 interrupts
 are allowed to do some system calls (activate a task, get a resource, ...)
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Kindly Note
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the execution time of an ISR must
be short because it delays the
execution of tasks.

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Interrupt
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ISR category 1 The ISR
does not use an operating
system service8. After the
ISR is finished,
processing continues
exactly at the instruction
where the interrupt has
occurred, i.e. the interrupt
has no influence on task
management. ISRs of this
category have the least
overhead.
ISR category 2 The OSEK
operating system provides
an ISR-frameto
prepare a run-time
environment for a
dedicated user routine.
During system generation
the user routine is
assigned to the
interrupt.

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Priority
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ISR1
Are not allowed to do system calls;
• ISR1 are ignored by the operating
system and defined as classical
interrupts:
• Init interrupt registers of the hardware
peripheral;
• Init the related interrupt mask
• Do not touch the other interrupt masks
(which are managed by the
operating system).

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Priority
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ISR2
May (must?) do system calls (activate a task, get a
resource, …)
• Roughly the same behavior as a task
• they have a priority (greater than the higher priority
of tasks).
ISR2 priority is a logical one and not be related to the
hardware priority level.
• they have a context (registers, stack, …)
• In addition an ISR2
• is associated to a hardware interrupt (triggered by an
event)
To use an ISR2, it is necessary to
• declare it in the OIL file with the interrupt
source identifier (depends on the
target platform) to indicate where the interrupt handler
is installed;
• initialize the related interrupt registers of the
peripheral which will trigger
the interrupt.

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ISR2
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Counters
and
Alarms
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Counters and Alarms
 OSEK/VDX Operating System Provides
support for processing recurring events.
 The recurring events (sources) are
registered by implementation specific
counters.
 Based on the counters the OSEK OS
provides alarm mechanisms to the
application.
34
Activate a task
Set an event

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Counters and Alarms cont.
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Goal:
perform an “action” after a number of “ticks” from an hardware device:
For example periodic activation of a task
with a hardware timer
Counter
Activate a taskSet an event

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The counters
 The counter is an abstraction of the hardware “tick”
source (timer, interrupt source, ...)
 The “tick” source is heavily dependent of the target
platform;
 The counter is a standard component;
 At least one counter is available:
SystemCounter
 No system call to modify the counters.
 Their behavior are masked by the alarms.
 A hardware interrupt must be associated to
a counter
36
CPU
Interrupt
controller
PIT
Periodic
interrupt
timer
Other
Modules
SOC

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The counters Cont.
A counter defines 3 values
37
The maximum
value of the
counter
(MaxAllowedValue)
The counter restart
to 0 after reaching
MaxAllowedValue
A division factor
(TicksPerBase):
for instance with a
TicksPerBase equal
to5, 5 ticks are
needed to have the
counter increased by 1;
(MINCYCLE)The
minimum number
of cycles before
the alarm is
triggered
Count = 0
Count = MaxAllowedValue
@count =
MINCYCLE alarm is happened

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OIL description of a counter
COUNTER generalCounter {
TICKSPERBASE = 10;
MAXALLOWEDVALUE = 65535;
MINCYCLE = 128;
};
38
number of “ticks” (from the interrupt
source) needed to have the counter
increased by one.
Count = 0
Count = 1
Count = 2
TICKSPERBASE = 10 ticks
Maximum value of the counter. This value is used by
the OIL compiler to generate the size of the variable
used to store the value of the counter
Count = MAXALLOWEDVALUE = 65535;
minimum interval between 2 triggering
of the alarm.

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The Alarms
 An alarm is connected to a counter
an performs an action.
 An alarm is associated to 1 counter
 A counter may be used for several
alarms
 When the counter reach a value of
the alarm (CycleTime, AlarmTime),
the alarm expires and an action is
performed:
 Activation of a task;
 Signalization of an event;
 alarm-callback routine
39
Activate a task
Set an event
alarm-callback routine

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Alarm-callback routines
Alarm-callback routines can have neither parameter nor return value.
The following format of the alarm-callback prototype shall apply:
ALARMCALLBACK(AlarmCallbackRoutineName);
Example for an alarm-callback routine:
ALARMCALLBACK(BrakePedalStroke)
{
/* do application processing */
}
The processing level of alarm-callback routines is the one used by the
scheduler, or ISR, depending on implementations
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Example
41
Delta time = 6
Delta time = 6 Delta time = 6

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Counters/Alarms
Counters d
Alarms may be started and stopped dynamicallyo not have system
calls.
 Alarms’ services
 SetAbsAlarm
 SetRelAlarm
 CancelAlarm
 GetAlarm
 GetAlarmBase
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SetAbsAlarm
StatusType SetAbsAlarm ( AlarmType <AlarmID>, TickType <start>,TickType
<cycle>)
 AlarmID is the id of the alarm to start.
 start is the absolute date at which the alarm expire
 cycle is the relative date (counted from the start date) at which the alarm expire
again• If 0, it is a one shot alarm
 StatusType is an error code:
 E_OK: no error;
 E_OS_STATE: The alarm is already started;
 E_OS_ID: The AlarmID is invalid.
 E_OS_VALUE: start is < 0 or > MaxAllowedValue and/or cycle is <MinCycle or >
MaxAllowedValue.
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SetRelAlarm
 StatusType SetRelAlarm ( AlarmType <AlarmID>, TickType
<increment>,TickType <cycle>)
 AlarmID is the id of the alarm to start.
 increment is the relative date at which the alarm expire
 cycle is the relative date (counted from the start date) at which the alarm expire
again. If 0, it is a one shot alarm
 StatusType is an error code:
 E_OK: no error;
 E_OS_STATE: The alarm is already started;
 E_OS_ID: The AlarmID is invalid.
 E_OS_VALUE: increment is < MinCycle or > MaxAllowedValue and/or cycle is < MinCycle
or > MaxAllowedValue.
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CancelAlarm
Stop an alarm.
 StatusType CancelAlarm (AlarmType <AlarmID>)
 AlarmID is the id of the alarm to stop.
 StatusType is an error code:
 E_OK: no error;
 E_OS_NOFUNC: The alarm is not started;
 E_OS_ID: The AlarmID is invalid.
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GetAlarm
 Get the remaining ticks before the alarm expires
 StatusType GetAlarm ( AlarmType <AlarmID>, TickRefType <tick>)
 AlarmID is the id of the alarm to get.
 tick is a pointer to a TickType where GetAlarm store the remaining
ticks before the alarm expire.
 StatusType is an error code:
 E_OK: no error;
 E_OS_NOFUNC: The alarm is not started;
 E_OS_ID: The AlarmID is invalid.
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GetAlarmBase
 Get the parameters of the undelying counter.
 StatusType GetAlarmBase ( AlarmType <AlarmID>, AlarmBaseRefType <info>)
 AlarmID is the id of the alarm.
 info is a pointer to an AlarmBaseType where GetAlarmBase store the parameters of
the underlying counter.
 StatusType is an error code:
 E_OK: no error;
 E_OS_ID: The AlarmID is invalid.
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OIL description of an alarm
48
ALARM alarm_1 {
COUNTER = generalCounter;
ACTION = ACTIVATETASK { TASK = task_1; } ;
AUTOSTART = TRUE {
ALARMTIME = 10;
CYCLETIME = 5000;
APPMODE = std;
};
};
action to be performed by the alarm.
Here, activation of task task_1.
The alarm is triggered à 10
It is a periodic alarm which is
triggered every 5000 counter tick

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Lab5 (Periodic task by Alarm)
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lab5
 Led 0 >>PORTA pin 4
 Led 1 >> PORTA pin 5
 Buzzer >> PORTD pin 7
 Write a periodic task (extended task) depends on Alram take action
(activate the periodic task ) with CYCLETIME = 512 counter cycles.
 The counter here is SystemCounter.
 The periodic task responsible on increment seven seg and toggle led 1
For each alarm.
 Also once the Count value reached to (x == 10|| x==30||x ==50||x==70||
x==90)
 Then will enable led 0 and the buzzer for only 1 count.
 The last thing change CYCLETIME and expect what happens ?
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Lab5 sequence
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Oil file 61

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Write the C code
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63Lab5.c

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Change the cycle time
in oil file and
see what will happen ?
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shared resources
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Accessing shared resources
 Hardware and software resources may be shared between tasks (an
optionally between tasks and ISR2 in OSEK).
 Resource management ensures that
 two tasks cannot occupy the same resource at the same time.
 priority inversion can not occur.
 deadlocks do not occur by use of these resources.
 two tasks or interrupt routines cannot occupy the same resource at the
same time.
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Example of an unprotected software resource
(global variable):
67
val may contain
2 … or 1
non
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Priority inversion on occupying
semaphores
 This means that a lower-priority task delays the execution of higher-priority task.
 sequencing of the common access of two tasks to a semaphore (in a full preemptive system, task T1
has the highest priority) Task T4 which has a low priority, occupies the semaphore S1. T1 preempts
T4 and requests the same semaphore. As the semaphore S1 is already occupied, T1 enters the waiting
state. Now the low-priority T4 is interrupted and preempted by tasks with a priority between those
of T1 and T4. T1 can only be executed after all lower-priority tasks have been terminated, and the
semaphore S1 has been released again. Although T2 and T3 do not use semaphore S1, they delay T1
with their runtime.
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semaphores
 In this case deadlock means the impossibility of task execution due to infinite waiting
for mutually locked resources
 The following scenario results in a deadlock: Task T1 occupies the semaphore S1 and
subsequently cannot continue running, e.g. because it is waiting for an event. Thus, the
lower-priority task T2 is transferred into the running state. It occupies the semaphore
S2. If T1 gets ready again and tries to occupy semaphore S2, it enters the waiting state
again. If now T2 tries to occupy semaphore S1, this results in a deadlock
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OSEK Priority Ceiling Protocol
 To avoid the problems of priority inversion and deadlocks the OSEK
operating system requires following behavior:
 At the system generation, to each resource its own ceiling priority is
statically assigned. The ceiling priority shall be set at least to the highest
priority of all tasks that access a resource or any of the resources linked
to this resource
 If a task requires a resource, and its current priority is lower than the
ceiling priority of the resource, the priority of the task is raised to the
ceiling priority of the resource.
 If the task releases the resource, the priority of this task is reset to the
priority which was dynamically assigned before requiring that resource.
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OSEK Priority Ceiling Protocol
(PCP)
 the mechanism of the priority ceiling.
Task T0 has the highest, and task T4
the lowest priority. Task T1 and task
T4 want to access the same
resource. The system shows clearly
that no unbounded priority inversion
is entailed. The high-priority task T1
waits for a shorter time than the
maximum duration of resource
occupation by T4.
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Resource assignment with priority ceiling between
preemptable tasks and interrupt services routines.
 To determine the ceiling
priority of resources which
are used in interrupts,
virtual priorities higher
than all tasks priorities are
assigned to interrupts
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Resource assignment with priority ceiling between interrupt
services routines
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OSEK resources
 OSEK resources are used to do mutual exclusion between several
tasks (or ISR2) to protect the access to a shared hardware or
software entity.
 Example of hardware entity:
 LCD display;
 Communication network (CAN, ethernet, … ).
 Example of software entity:
 a global variable;
 the scheduler (in this case, the task may not be preempted).
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OSEK resources Cont.
 OSEK/VDX offers a RESOURCE mechanism with 2 associated system
calls:
 GetResource
 ReleaseResource
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GetResource
 StatusType GetResource ( ResourceType <ResID> ) ;
 Get the resource ResID;
 StatusType is an error code:
 E_OK: no error;
 E_OS_ID: the resource id is invalid;
 E_OS_ACCESS: trying to get a resource that is already in use (it is a
 design error).
 A task that « own » the resource may not be preempted by another
task that will try to get the resource.
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ReleaseResource
 StatusType ReleaseResource ( ResourceType <ResID> ) ;
 Release the resource ResID;
 StatusType is an error code:
 E_OK: no error;
 E_OS_ID: the resource id is invalid;
 E_OS_ACCESS: trying to release a resource that is not in use (it is a
 design error).
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Tasks group
 This feature allow to mix non-preemptable tasks and preemptable
tasks.
 In the same group all the tasks are seen as non-preemptable by the other
tasks of the group.
 A task having a higher priority of all the tasks of the group (and not part
of the group) may preempt any task of the group.
 This feature uses an internal resource for each group:
 The internal resource is got automatically when the task start to run;
 The internal resource is released automatically when the task terminates;
 An internal resource may not be reference with GetResource() or
ReleaseResource().
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OIL Description of a resource
RESOURCE resA {
RESOURCEPROPERTY =
STANDARD;
};
79
TASK myTask {
PRIORITY = 2;
AUTOSTART = FALSE;
ACTIVATION = 1;
SCHEDULE = NON;
RESOURCE = resA;
STACKSIZE = 32768;
};

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Lab6: Resources (expect what the
output and draw the task timeline)
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Oil file
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Lab6.c 82

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Lab6 solution
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Lab6 solution
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Lab6 solution
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Lab6: Resources (expect what the
output and draw the task timeline)
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Oil file
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Lab6.c 88

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Lab6 solution
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Lab6 solution
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Lab6 solution
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In the next session will take
Communication in OSEK/VDX OS
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References
 Embedded Microcomputer Systems Real Time Interfacing Third
Edition Jonathan W. Valvano University of Texas at Austin.
 MicroC/OS-II the real-time kernel second edition jean j.labrosse.
 RTOS Concepts http://www.embeddedcraft.org.
 OSEK/VDX Operating System Specification 2.2.3
 AUTOSAR Layered Software Architecture
 The Trampoline Handbook release 2.0
 Trampoline (OSEK/VDX OS) Test Implementation -Version 1.0,
Florent PAVIN ; Jean-Luc BECHENNEC
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References
 Trampoline:an open platform for (small) embedded systems based on
OSEK/VDX and AUTOSAR
http://trampoline.rts-software.org/
Jean-Luc Béchennec1;2, Sébastien Faucou1;3
1IRCCyN (Institute of Research in Communications and Cybernetics of Nantes)
2CNRS (National Center for Scientific Research) / 3University of Nantes
10th Libre Software Meeting
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References
 Real Time Systems (RETSY)
Jean-Luc Béchennec - Jean-Luc.Bechennec@irccyn.ec-nantes.fr
Sébastien Faucou - Sebastien.Faucou@univ-nantes.fr
jeudi 12 novembre 15
 AUTOSAR Specification of Operating System V5.0.0 R4.0 Rev 3
 OSEK - Basics http://taisnotes.blogspot.com.eg/2016/07/osek-
basic-task-vs-extended-task.html
 OSEK OS Session Speaker Deepak V.
M.S Ramaiah School of Advanced Studies - Bangalore 1
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