[etherlab-users] application modules

[Gavin Lambert]

As I understand it, traditionally RT apps had to be kernel-mode because it simply wasn’t possible to write a userspace app with the latency guarantees that are required.  Hence also the use of RT co-kernels.  That has improved considerably in recent years, and it’s now easier to make a reliable userspace app – but for tight cycle times or if missed cycles can have safety consequences, it might still be better to use an RT co-kernel.

You can’t have multiple userspace processes sharing networks, however.  Once an application “claims” a master interface for realtime use (to bring slaves to OP and exchange PDOs), no other processes can do so.  It is, however, still possible for other processes to queue SDO requests and a few other non-realtime things, but even this is preferably gatewayed through the app so that it knows what is going on.


Gavin Lambert
Senior Software Developer

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From: William Zumwalt
Sent: Saturday, 3 August 2019 03:57
To: etherlab-users at etherlab.org
Subject: [etherlab-users] application modules

The only reason I can think of for wanting to write an app as a KM is if data weren't going to userspace, but back down the network stack (using another protocol?). My process data needs to go into userspace and I'm also curious how an app written as a KM would send it's data to userspace?

According to the docs, the only difference I see is external memory for domains. In the case of not having a single app mod instance, could there be issues in multi-threading, having multiple user-space processes write to the same PDO?

Can anyone think of any good reasons for writing the app as a KM?

Will
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