Gui timer v/s Async timer priority

Question

Hi NI,
I am trying to build an application where in i am communicating with an automotive ECU over RS-232 periodically. I am using an aysnc timer to do the communications part and a GUI timer to do the graphical object update. I have three questions for your team.
1. What RTOS and PC configuration do you recommend for using a RT Async Timer with Prority ? (preferably whats available in the market today in terms of "cheap" hardware)
2. What is the priority of the GUI timer when compared to the Async timer? Is is possible for the GUI timer to inetrrupt the Async timer fucntion call ? If yes...is there an exclusion mechanism that would stop this from happening ?
3. I am using a two linked list concept...the first list populates while the other's data is being drawn on the strip chart...and then i flip over to populating the second linked list while the first lists data is being plotted. The communications(population of data in a structure in a linked list) is being done in the Async thread while the plotting is being done in the GUI thread. The issue i am facing is that i do not have a clean linked list population, plotting and freeing of data sequence...i feel this is due to some un-predictability in the timer function calls.(hence Q2 above). Do you recommend only using thread safe queues or do you think this is do-able with linked lists.
Looking forward to your reponse.
-Ashish

Answer 1

I don't know what degree of certainity you need but a "fixed calling and execution sequence" is just a dream in a Windows environment.
Windows will operate your threads together with many more of its own, all with varying priorities.
So, you should think of priority as a vague way of making one thread to be operated more/less than another lower/higher degree thread.
No thread priority class guarantees a certain frequency of thread execution.
GUI timer callbacks are executed in the main program thread while async timers are executed in a seperate thread.
So, yes their execution times may coincide. Hence the need to protect your global data.
Data accessed by multiple threads should be protected so that, no thread would be interrupted in the middle of a write/read operation on that data.
TSQs do that for you. Otherwise you cannot be sure about the integrity of the data you are plotting.
If you need do some more reading about this. But TSQs stand out as a more elegant way to solve your problem.
S. Eren BALCI
www.aselsan.com.tr