What to Expect for the CLED Exam
Last week I got my student head on again to take the Certified LabVIEW Embedded Systems Developer (CLED) exams and want to let you know what to expect if you are thinking about taking the exam, or if you are wondering if it is for you?
The What and the Why
NI introduced the CLED certification last year as a pilot exam in the US and is now available in Europe (and possibly other regions). It’s a 2 part exam to test your knowledge of using RT and FPGA technologies with a massive emphasis on compactRIO embedded applications.
As a self-proclaimed LabVIEW embedded developer I am very happy this has been introduced (as I can remove the “self-proclaimed”!).
There are a huge number of developers using LabVIEW under Windows for test and measurement applications who are very skilled and may well be CLD or CLA, but this doesn’t mean too much when it comes to RT and FPGA. If you don’t understand the differences and subtleties of these then you can get yourself in a mess.
The CLED allows embedded LabVIEW developers to differentiate themselves and differentiation means your next pay rise/promotion/job.
So what can you expect?
Before you even open the prep kit make sure you have the pre-requisites which seem to be more involved on this exam than may, as I will explain though don’t be frustrated, if you don’t have these pre-requisites you may well waste your time going through the process to find you aren’t ready yet.
From the NI site:
– Valid Certified LabVIEW Developer (CLD) or Certified LabVIEW Architect (CLA) certification
– Completion of LabVIEW Real-Time 2: Architecting Embedded Systems or RIO Integrator’s Training course
– Completion of the LabVIEW FPGA training course
Recommended Experience Level
– 18 to 24 months of experience in developing medium- to large-scale LabVIEW control and monitoring applications with NI CompactRIO, NI Single-Board RIO, and/or NI R Series hardware
If you don’t meet these then there is your first task!
Part 1: Multiple Choice
Your first test is a 1hr multiple choice exam à la CLAD. You must pass this with a 70% result before attempting part 2.
It tests the theory aspects of developing for RT and FPGA on compactRIO all the way from deciding how to configure the hardware to how loop priorities work. I did find it a little more conceptual than the CLAD, less “what is this function” and less triple negatives to decode the answer.
Because of my time at NI I didn’t find this element too stressful, having taught the courses for a few years you get familiar with the nuances of these things but there are some resources I found very useful:
- CLED Practice Exam: It goes without saying that the sample exam is useful. Also there is a link to a video of a prep presentation at NI Week last year.
- cRIO Developers Guide: I would suggest this is probably the bible for part 1. I think that probably every question could be answered in here (though I haven’t checked)
I think the key challenge here is that you must make sure you have broad knowledge on cRIO. For example there are questions in the sample exam on selecting whether to run FPGA mode or scan mode (or hybrid) which I expect many developers may not have come across too often. There are also questions on other more niche topics such as FPGA optimisation, advanced shared variable settings and there will certainly be questions around functions that cause or prevent dynamic memory allocations.
Part 2: Practical Exam
Yep, another 4 hour practical exam but somehow it is different again!
I must admit I was a little dismissive of this initially. Having done the CLD and CLA, as well as training many people on how to take the CLD exam through CLD prep days I was fairly confident I knew how to tackle these exams, this lasted up until about an hour into my practice exam when I realised the emphasis changes again.
The practical exam is an application development problem which you deploy onto a single-board RIO which is connected to a simulator. You must write the host code (front panel provided), RT and FPGA according to the requirements provided, these are more similar in scope to the CLD rather than being as heavy as the CLA requirements. The clue to the key difference is the marking scheme:
- 50% Functionality
- 30% Design
- 15% Style
- 5% Documentation
Compared to the other exams functionality is massively more important, you could have rubbish style and documentation (although I hope you wouldn’t at this stage) and still get 80% on the exam.
This was my first error, in my practice exam I was working to get my style to the level that I would for the CLD exam but there simply isn’t time.
In fact time is incredibly tight, I think with another 30-60 mins I may have had time to get the functionality done and tested. From looking at the sample solution as well the attitude I took towards it is to treat it as a well designed prototype, what I mean by this is things like:
- Design is important. Those 30% should be the easy ones to pick up as even just starting functionality in the right places with the right communication methods should win marks quickly.
- Style is less important. With 4 hours to create an end to end solution something has to give and this is it. Don’t go back to pre-CLD, I still used non-default icons, modularised and commented where appropriate but there isn’t time to design nice libraries and nitpick.
- Take every requirement short cut. You can see this in the sample exam solution, if they don’t explicitly ask for it, use whatever route makes your life easier. Obviously in real life there is some value in predicting what a user might ask for next and account for it, that will never happen with the exam!
I think there are probably two different approaches to the exam:
The Horizontal Approach
This would mean completing the FPGA functionality, then building the RT on top of that and then the host.
There is some advantage that then you don’t have to switch context too often which may be less efficient. You can also get your FPGA compile out of the way although I found mine to be <10 minutes anyway.
It also means you hit some of the key aspects earlier, I think every exam is probably going to need a watchdog, maybe safe states, recovery ability and this is all going to be lower level functionality which you can get out of the way first.
My concern with this approach was that it could depend how it is marked. Technically many features need functionality at every level which may make this more risky on time. You could probably mitigate this by laying out your design first (and getting those design points) so even if you don’t get the UI bit done it is clear how you would.
The Vertical Approach
This is what I opted for. I took each section of the requirements document and implemented the full requirement from top to bottom before moving the next section.
This has the advantage of being able to fully tick off requirements earlier, it is easier to test that it is working one step at a time and I just find it a way of coding that builds confidence as you move forward, but don’t think this worked flawlessly!
The first problem is those design points. I laid out much of the design to start anyway so that those points are done, this also helps move this approach forward so you’re not having to make higher level design decisions as you go. I do wish I had jotted these down so that I can put the paper in the envelope as well to show the design (presuming these get looked at).
The main issue with this is deciding how to prioritise the features. I had a success with this and a failure.
The success was one feature that was very easy to implement and fitted my design well. Because of this I set this at a low priority and never implemented it. The reason I am happy with this was that I hope the design was obvious, I documented the changes needed for it and freed up my time for other tasks where this would have been harder. Hopefully I still got some marks for my intentions though.
The failure was some of the core features such as my watchdog. There was one chunk of the application that worked on start to finish (which too 1-1.5hrs so a big piece). This didn’t leave me much time when I moved onto the fault handling including the watchdog. I got it in but only just and not well tested. I should have split the larger task, again documenting where advanced features would go and moved onto the more core watchdog functionality.
Did I Pass?
I don’t know. Obviously I passed part 1 to attempt part 2, now I’m in the waiting game for the results. If I had to guess I think I would put my chances for passing at about 75% I reckon but lets see. I was much happier with the real exam but I definitely ran out of time which will affect my functionality marks and could have done with making the design decisions more obvious with documentation. We will see!
If you’re attempting the exam, good luck and I hope this was useful. Once you have tried it or got your results please comment below on how you did and any more tips you may have, it would be great to here what approaches other people took.