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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


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

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
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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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