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1 LOG_printf(&trace,"TSK0 Start");

In the table, the TSK0 is in the TSK_RUNNING (E) state, TSK1 is in the TSK_READY (R) state, the semaphore has a value of 1 and the line causes the output "TSK0 Start". The next line of code to execute is

2 SEM_pend(&SEM0,SYS_FOREVER);

The other states for the tasks are TSK_BLOCKED (B) and TSK_TERMINATED (T).

Code Line # TSK0 State TSK1 State SEM0 Output
1 E R 1 TSK0 Start
2 E R 0
3 E R 0 TSK0 1
4 B E 0
5 B E 0 TSK1 Start
6 R E 0
7 R E 0 TSK 1
8 R E 1
9 R E 0
10 E B 0
11 E B 0 TSK0 2
12 E R 0
13 E R 1
14 E R 1 TSK0 3
15 E R 2
16 E R 2 TSK0 Finish
17 T E 2 TSK1 2
18 T T 2 TSK1 Finish

Semaphore as a resource monitor

There are a couple common practical uses for semaphores. One of those uses is to count how many items are on a queue. The other is to restrict tasks from accessing a resource at the same time.

Queue count

Suppose there are two tasks in your system, TSK_Send and TSK_Receive and there is one queue between them, QUE0. To keep track of how many elements are on the queue there is a counting semaphore, SEM0. The semaphore is initialized to 0. See Figure 1.

Tasks and queue

When TSK_Send puts a message on the queue, it will perform a SEM_post(&SEM0) which will increment the count on the semaphore. Before the TSK_Receive tries to get a message off the queue it will perform a SEM_pend(&SEM0,SYS_FOREVER) . This will decrement the count on the semaphore every time the TSK_Receive takes a message off the queue. If there are no messages on the queue, SEM0 will be 0 and the task will block. This will cause the task to wait until the TSK_Send task puts another message on the queue.

Resource sharing

When two tasks share a resource, it may be necessary for the tasks have mutually exclusive access to the resource. In this case, a semaphore can be used to acquire access to the resourse or lock access to a resource.

Suppose there are two tasks with the same priority in your system, TSK0 and TSK1. There is a Resource that the two tasks share. A semaphore, SEM0, will be used to aquire access to the resource. The semaphore is initialized to 1. See Figure 2.

Two tasks sharing a resource

In order for the tasks to have mutually exclusive access to the resource, each task must perform a SEM_pend(&SEM0,SYS_FOREVER) before using the resource and a SEM_post(&SEM0) after using the resource.

Examine the following code that does NOT use a semaphore when writing to the resource.

int Resource[4];Void funTSK0() {Resource[0]=0;Resource[1]=1;TSK_yield(); Resource[2]=2; Resource[3]=3; }Void funTSK1(){ Resource[0]=4; Resource[1]=5; Resource[2]=6; Resource[3]=7; }

When the tasks finish the contents of the array Resource will be [4,5,2,3]. Clearly, we would like it to be either [0,1,2,3]or [4,5,6,7]. To fix this, add the semaphore.

int Resource[4];Void funTSK0() {SEM_pend(&SEM0,SYS_FOREVER); Resource[0]=0; Resource[1]=1; TSK_yield();Resource[2]=2;Resource[3]=3;SEM_post(&SEM0); }Void funTSK1(){ SEM_pend(&SEM0,SYS_FOREVER); Resource[0]=4; Resource[1]=5; Resource[2]=6; Resource[3]=7; SEM_post(&SEM0); }

When the tasks finish the contents of the array Resource will be [4,5,6,7]. The reason for this is that after TSK0 performs a TSK_yield , TSK1 tries to perform a SEM_pend but gets blocked. At that point TSK0 continues running and finishes with the resource. Then TSK1 begins to run and writes the complete array.

Viewing objects

Whe debugging a project it is important to see the characteristics of the components in your project. When using DSP/BIOS in CCS it is possible to view the DSP/BIOS objects and their properties using the RTSC Object Viewer (ROV). RTSC is Real Time Software Components which is a standard for developing software modules/libraries.

To view the DSP/BIOS v5.x objects and properties in the debug mode, select Tools->ROV . This will bring up a window that looks like the following figure.

RTSC Object Viewer

This figure shows the SEM module and the semaphore in the project. Notice the different properties that can be seen for each semaphore.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Ti dsp/bios lab. OpenStax CNX. Sep 03, 2013 Download for free at http://cnx.org/content/col11265/1.8
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