11/24/2016 11:09 AM | |
Joined: 9/23/2005 Last visit: 9/20/2024 Posts: 4707 Rating: (721) |
IMHO, saying that something is 100x longer means nothing. Why? Because 100 x (almost nothing) is still almost nothing. Next thing is that PIP update by the OS is not instant and it adds up to a execution time of an application as well. In case of 314C's on-board AIs, the single input access is ca. 5 us (u as micro). All 4 -> 20 us. And usually it's enough to read once per cycle (and then store it locally if it's to be accessed multiple times). Finally, let's assume that your OB35 logic will need execution time of 1 ms every 5 ms. Then because of IO access from 1000 us you will get 1020 us. I see no big difference. The only problem is that when you read all the inputs even one after the other, some of them can be 1 ms older then the others (i.e. they can be not from the same point in time). But not knowing your application it's hard to judge if it's real problem. Anyway, I think using PIP doesn't solve it either. But this I'm not 100% sure. The numbers presented can be found here. BTW, I think there's a coding trick which in this case should allow to read the inputs in ca 13 us. So, when you become desperate about the execution time you may wish to find it. |
Regards, |
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11/24/2016 3:16 PM | |
Joined: 4/23/2015 Last visit: 6/12/2023 Posts: 168 Rating: (9) |
Hi, Jacek, Agreed with everything what you're saing in your most recent post. Regarding peripheral access time I've reffered to this article, which says that L IB x 0.05 μs L PIB x 15.01 μs Of course, I will try PQW/PIW, I didn't try it yet. Just want to make sure first why PIP1 doesn't work. Could you please also give more comments on your note about 13us I/O read. What is it? |
Last edited by: _Pavel_ at: 11/24/2016 3:17:50 PM |
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11/24/2016 3:40 PM | |
Joined: 9/23/2005 Last visit: 9/20/2024 Posts: 4707 Rating: (721) |
It's nicely omitted that the data must be copied to the process image first. I have no rock solid explanation for this, but I think that it's reserved for OB61. Have you sent a Service Request to clarify situation at the source (i.e. Siemens)? |
Regards, |
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11/24/2016 5:35 PM | |
Joined: 4/23/2015 Last visit: 6/12/2023 Posts: 168 Rating: (9) |
No. |
11/26/2016 6:01 PM | |
Joined: 6/24/2013 Last visit: 9/20/2024 Posts: 1628 Rating: (421)
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Contgratulations:-) Glad You have solved the issue and it works fine. |
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