USB- Serial good info

[JÞB]

OK so I just spent a day debugging an app that had an insidieous race condition and thought I'd share a bit.

The system communicates with a DUT using a USB- Serial adaptor with theFTDIser driver installed.  what I saw was sub-vi's that each completed fine on there own however when run from the "test" system I saw some timeout errors. 

Adding delays had limited effect however breakpoints and property nodes both solved the issue (so of course I suspected I was insane)

So I ran across this rather interesting post.  and yes- I used async calls to VISA read and VISA Write.  AHhhh async calls do NOT force async behavior only request async behavior!  so I looked into latency of the ftdi driver here and here.

with the async calls I managed to race follow-up VISA calls by starting the second function BEFORE the first completed and locked up the interface.  The Breakpoints and property nodes FORCED a switch to th UI thread and the async calls completed synchronously.  

Replacing the VISA calls with synchronous calls saved my bacon. (at some time penalty) 

[Steven_T]

Jeff,

I'm sure others will find this information very informative and will save others in this community quite a bit of time!

Thanks for the post!

Steven T.

[JÞB · Accepted solution]

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Steven T wrote:

Jeff,

I'm sure others will find this information very informative and will save others in this community quite a bit of time!

Thanks for the post!

Steven T.

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Yes, And i've found a great place to save links to the tech documents that I'd otherwise spend hours looking for when I need to get down to this level again (say in 2-3 years)