systemAutomotive Embedded Systems part4(OSEK OS).

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Automotive Embedded
Systems part4
(OSEK OS).
ENG.KEROLES SHENOUDA
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OSEK/VDX
Operating System
it's time to wake up 
Learn In Depth 
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Conformance
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 In order to allow OSEK-OS to be used in a variety of systems with
different capacities and demands (for example memory, processing
capacity, etc.) is that OSEK-OS defines 4 classes of compliance (CC).
 Conformance classes are determined according to the following
attributes:
 Multiple activation of basic tasks
 Types of tasks accepted: basic and extended
 Number of tasks by priority
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Hook Routines
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Hook Routines
 The hookroutines are functions implemented by the user that the
operating system will call in specific situations.
 They are optional and can be used to add some specific management desired
by the user in the following situations:
 StartupHook: it is called during the initialization of the operating system,
before being completed.
 ShutdownHook: it is called at the end of the shutdown of the operating system.
 PreTaskHook: is called before proceeding to execute a task. •
 PostTaskHook: is called when the execution of a task ends.
 ErrorHook: it is called in case any of the interfaces of the operating system
returns a value other than E_OK.
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Hook Routines
 Features
 OSEK proposes dedicated routines (or functions) to allow the user to
«hook » an action at important stages in system calls.
 “hook routines” are/have:
 called by the operating system;
 a priority greater than all tasks;
 not interrupted by ISR2 (presented after);
 a standardized interface;
 able to call a subset of the operating system services.
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StartupHook
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is called after the
startup of the OS
but before the
startup of
the scheduler

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StartupHook example
 1.After completing the initialization of C, the main
function is called, the same in this case proceeds to
start the execution of the operating system in 2.
 3 Once the initialization of the operating system,
the same calls StartupHook.
 4 Just when you start StartupHook starts the
Scheduler and it proceeds to run Tasks
9
1.For the operating system to call
the StartupHook, the same should be
indicate by setting STARTUPHOOK to
TRUE
2 Just after calling Startup-
Hook the operating system will proceed
to start the Scheduler, so the task
InitTask will be executed after
StartupHook

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PreTaskHook and PostTaskHook
 PreTaskHook and PostTaskHook
 PreTaskHook is called just before a task goes from READY state to
RUNNING state;
 PostTaskHook is called just before a task goes from RUNNING state to
READY or SUSPENDED state;
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PreTaskHook example
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For the operating system to call the
PreTaskHook, the same should be
indicated configuring the
PRETASKPHOOK parameter TRUE.

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PostTaskHook example
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For the operating system to call
the PreTaskHook, the same should be indicated
configuring the POSTTASKPHOOK parameter
TRUE.

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ErrorHook
 This routine called when a system call does not return E_OK, that is if
an error occurs during a system call.
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ErrorHook
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For the operating system to call
the ErrorHook, the same should be indicated
configuring the ERRORHOOK parameter
TRUE

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handling (extended status)
 The macro OSErrorGetServiceId() provides the
service identifier where the error has been
risen.
 the macros to access the parameters of
SetRelAlarm are:
 OSError_SetRelAlarm_AlarmID()
 OSError_SetRelAlarm_increment()
 OSError_SetRelAlarm_cycle()
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ShutdownHook
16
1 In case an error has not
occurred,
Error parameter will have
the value E_OK.
2 ShutdownHook is called
from
ShutdownOS, therefore it is
necessary to turn off
the system so that it is
called.
For the operating system to call the
ShutdownHook, the same should
be indicated
configuring the SHUTDOWNHOOK
parameter TRUE.

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levels of error
 OSEK-OS offers two levels of error checking that can be
configured in the .oil file
 extended: it is the mode used during development. Some
extra checks are made and returned in case of error.
standard: this is the mode used in production. Only very
critical errors are detected and reported.
 In this Example, "Error handling" is used the ActivateTask
interface that can return E_OK, E_OS_LIMIT or E_OS_ID
when the level of the error check is set to extended
 but only E_OK and E_OS_LIMIT when the level of error
checks It is established to standard.
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Resources Concepts in RTOS
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Shared Data between Tasks
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how does the consumer know that (new) data is available?
Data is shared between several tasks and, in
order to keep the data in a consistent state,
we need to protect it from concurrent
access. In other words: access to the data
must be serialized.
This use case is mainly about task synchronization:
the interplay between producer and consumer must work
smoothly. How does a consumer know that new data is
available?
how to serialize access to shared data?

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Two shared Resource Control
20
the mutex = MUTual EXclusion.
the semaphore
Resource
A resource is any entity used by a task. A resource can thus be
an I/O device such as a printer, a keyboard, a display, etc. or a
variable, a structure, an array, etc.
Shared Resource
A shared resource is a resource that can be used by more than one task. Each task should
gain exclusive access to the shared resource to prevent data corruption. This is called
Mutual Exclusion.

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the mutex
 A critical section is a piece of code (part of a
function) from which the access to the shared
resource must be atomic. At a certain moment in
time, one and only one critical section is allowed to
access the shared data
 The mutex implements two operations:
 acquire: enter the critical section, or sleep if another
task has already acquired the mutex, and
 release: leave the critical section. Other tasks now
have the possibility to acquire the mutex.
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the mutex
 The concept of ownership is very important
here: the task that acquired the mutex must release
it as well.
 techniques to address mutual exclusion include:
 disabling/enabling interrupts
 disabling scheduling
 performing test-and-set operations (indivisibly)
 using semaphores
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Mutual Exclusion
Disable interrupts Mechanism
 Demand: exclusive use of a resource
 Disable interrupts
 Used on critical sections of code
 disabling/enabling interrupts
 used to access a few variables or small data
structures
 used when the process time is minimal
 affects interrupt latency
 you should not disable interrupts for any longer
than the kernel does
 in C/OS-II:
OS_ENTER_CRITICAL( );
… // you can access shared data here
OS_EXIT_CRITICAL( ):
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Mutual Exclusion
Disable interrupts Mechanism
24
So if a shared resource is shared
between a task and an interrupt
service routine, then the task can
disable interrupts before entering the
shared resource. This will stop the ISR
from accessing the shared resource
Disadvantages:
1. Disabling interrupt for long time
harm the system response
And the RTOS Kernel Itself

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Disable preemption (Task Switching) Mechanism
25
disabling scheduling
instead of disabling all maskable interrupts, you may just
want to disable the scheduler
an interrupted task is returned to, not necessarily
the highest priority task
implies that data is not shared with the ISRs
in C/OS-II:
OSSchedLock( );
… // you can access shared data here
OSSchedUnlock( );

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performing test-and-set operations (indivisibly)
 perform test-and-set operations (indivisibly)
 two tasks may agree that to use a common
resource, they must first check a global
variable
 while it is being checked, and before it is set,
by one task, it must be made inaccessible by
the other
 this can be achieved by:
 disabling interrupts (above) or
 some processors now support a single TAS
instruction
 Make the following
test test-and-set variable
Set test-and-set variable to 1
Access resource
Set test-and-set variable to 0
26
Kindly Note: DPRAM test-and-set instructions can
work in many ways
When CPU 1 issues a test-and-set instruction, the
DPRAM first makes an "internal note" of this by
storing the address of the memory location in a special
place. If at this point, CPU 2 happens to issue a test-
and-set instruction for the same memory location, the
DPRAM first checks its "internal note", recognizes the
situation, and issues a BUSY interrupt, which tells CPU
2 that it must wait and retry.

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SEMAPHORES | Operating System
(Simplified)
27
https://www.youtube.com/watch?v=PQ5aK5wLCQE

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Mutual Exclusion - semaphores
 a protocol mechanism to control
access to shared resources, signal
the occurrence of an event or allow
two tasks to synchronize
 one analogy is that in order for a
task to use a resource it must first
draw a key for it
 if the key(s) is in use, the task
suspends
 wait on (pend) & signal (post)
semaphore
 two types of semaphores:
 binary and counting (general)
28
task 2
task 1 1. pend
4. post
Printer
2. pend
6. post
5. “my name is task 2”
3. “my name is task 1”

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Mutual Exclusion - semaphores
29
 accessing shared data in C/OS-II
OS_EVENT *SharedDataSem;
SharedDataSem = OSSemCreate(1);
...
void Function (void) {
INT8U err; //read as “char *err” (string)
...
OSSemPend(SharedDataSem, 0, &err);
… //access shared data
OSSemPost(SharedDataSem);
}
binary semaphore
timeout value
{wait forever in this case}
error message code

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OSEK-OS Resources Concepts
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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):
33
val may contain
2 … or 1
non
determinism

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Resources
 If two applications simultaneously use a resource such as being a data bus
or a port but they do not synchronize with each other, the result can be
indeterminate.
 For this reason, in order to access resources, conventional traffic lights
are used or mutex to be able to access them from several tasks without
generating interference or collisions between them. However, the use of
traffic lights and mutex have two problems:
 inversion of priorities: occurs when a relatively high priority task must be
blocked by requiring the use of a resource that is being used by a priority task
minor that was interrupted to execute the highest priority task.
 deadlocks: occurs when two tasks use two resources (or semaphores) in
reverse order blocking each other. OSEK-OS offers a solution for accessing
resources that avoids both these problems.
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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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embedded_systemDeadlock situation using
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;
};
46
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 49

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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 55

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Lab6 solution
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Lab6 solution
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Lab6 solution
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The Scheduler as a resource
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“RES_SCHEDULER” Resource
 There is a resource that is always available for tasks and is
the RES_SCHEDULER.
 By using this resource a PREEMPTIVE task can block any
other while it is performing an action during which does not want to be
interrupted.
 In this way it is possible for a PREEMPTIVE task transforming itself
during the use of this resource into a NON PREEMPTIVE task.
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Using RES_SCHEDULER
 "Using RES_SCHEDULER" you can see that
the DemoTask task has been configured as
PREEMPTIVE, and therefore You can use the
resource RES_SCHEDULER.
 The use of the RES_SHEDULER resource from a
NON PREEMPTIVE task has no meaning,
it will not be interrupted by itself by no other,
regardless of whether or not it uses the resource
RES_SCHEDULER.
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Internal Resources
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Internal Resources
 OSEK-OS offers the possibility of defining internal resources.
 These resources are not handled and released by using GetResource and
ReleaseResource but they are automatically reserved and released by
the system at Begin and finish a task.
 By using internal resources the user is allowed to create task groups
cooperatives which use the same internal resource. In this way all the tasks that
use the same internal resource behave each other as NON PREEMPTIVE.
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Internal Resources
Example
 As you can see "Using internal resources" the
task DemoTask1 during its processing will never be
interrupted by DemoTask3, despite of this having a
priority of 5 and this is greater than the priority of
DemoTask1 which is 1.
 Both DemoTask1 and DemoTask3 will have a priority of
5.5 when running "OSEK Priority Ceiling Protocol").
 However, DemoTask1 may be interrupted by DemoTask2
that has a priority of 3, since it does not use the internal
resource.
 DemoTask3 will be able to interrupt DemoTask1 if it
calls Schedule when DemoTask3 is in the ready
state. In this way it is possible to arm groups of tasks
that do not interrupt each other, or interrupt only
explicitly when the user calls Schedule.
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Linkead os Resources
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Linkead os Resources
 Linking two resources is linked
internally so that for the operating
system They have different
names but they are treated as if
they were the same resource.
 In this Example, "Using Linked Resources"
you can see two TaskA tasks and TaskB
using respectively Res1 and Res2. The
operating system treats both resources as
if they were the same.
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Prepare your self for the next
session
(AUTOSAR OS)
#LEARN_IN_DEPTH 
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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
 Introducción a OSEK-OS - El Sistema Operativo del CIAA-Firmware
Programación de Sistemas Embebidos
MSc. Ing. Mariano Cerdeiro
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