Serial asynchronous architecture

Hi,
I have a problem with which way would be best in terms of some architecture. At present I have an existing program which consists of 4 asynchronous loops running in parallel. Each loop is a state machine which is controlled via a global notifier to start the state machine off. I also have 4 Marposs digital acquisition systems for which i have written the Drivers from scratch using VISA. All of these marposs devices communicate through 1 serial port. I have successfully, in isolation managed to acquire data using the three vi's listed below.
- Start Acquisition (Start.vi)
- Read Digital Array Values (Read.vi)
- Stop / reset Acquisition (Stop.vi)
This gives me data acquired from the device timed in the hardware at say 0.25mS/Sample (Which i need this speed)
The problem I have is in putting this same process into each of the 4 mentioned asynchronous loops. I know they will cause conflict as they stand. However I was thinking of putting the Acquisition into a Daemon and only executing the acquisition (With a notifier / rendezvous) when all stations are ready for measurement. This I have done in the past however I believe this could have an adverse impact on throughput, which is already close to specification Limits.
Another method maybe to put the subvi's into some kind of wrapper which has some kind of access control?
Is it possible to put each of the Marposs devices onto a virtual Serial Port? even though they use one Physical Port? <-- Long shot but would be nice!
I am hoping someone has already had a similar problem to this before and can advise me on the proper way forward. If not i think i will go ahead and go down the daemon route, which i am not too keen on doing.
Thanks in advance
Craig
LabVIEW 2012

Hi, Thanks for the Questions.
The Units are on a RS485 bus going through a USB adapter (Not Ideal). The units used to be polled in a similar fashion you suggested. However this is not enough for our needs as we need to profile the measurements for better accuracy and post processing etc. What the new method needs to do is Tell that probe to start Acq, wait untill part / movement has been made then collect that data from the FIFO within the hardware. At the moment there are 3 low level vi's that have this functionality but I am having trouble trying to see how these might go into a Daemon type polling loop which can supply all 4 asynchronous stations. Each station is in effect a state machine which sets a bunch of automation controls in a sequence then "Measures"using the Marposs devices so I suppose the timing for the acquisition is indeterminant to a degree unless some sort of notifieris used.
LabVIEW 2012

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CNiVisaSession::Read() Serial asynchrone, is it possible?

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System: Measurement Studio 6.0
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Alain:
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Senior Software Engineer, NI-VISA
National Instruments

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Hummmm.... That's too bad for me :-(
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Pipilined block with latches driven by different clock in FPGA

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Regards,
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Message Edited by jdigiova on 04-17-2007 04:52 PM
Attachments:
PipelinedSCTLArch.JPG ‏95 KB

How to get server data without reading from the socket stream?

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Best architecture for testing multiple (8) serial devices

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As tbob pointed out, the architecture will be fully dependent on the exact details of the problem. That being said, I do have my two cents to put in. In my work, I deal a lot with serial communication (too much, in my opinion); in some instances, I am dealing with the same device on different machines and in other instances, different devices talking on different ports on the same machine. Regardless of what the implementation is, you will find that there is a lot of commonality to be found in serial IO (open port, close port, configure port, send ascii command, receive ascii data, block simultaneous attempts to R/W, etc, etc) that is really independent of implementation. To me, this just screams for an object-oriented approach. The ability to reuse or change the details of the code while limiting changes to the interface itself is awesome. In your case, if you have 8 similar devices, I see 8 instances of a class which inherits properties from a Serial IO superclass; if we are dealing with different types, then you can exploit the inheritance features of objects to basically call 8 instances of different children of the Serial IO superclass.
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Matt Richardson
Certified LabVIEW Developer
MSR Consulting, LLC

Problems with asynchronous visa read with USB to serial port adapter

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Asynchronous serial input with an sbRIO FPGA

Background:
As part of my capstone project, I'm trying to read data transmitted serially from an IMU. The host is an sbRIO 9602.
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As an aside, I've only been working with LabVIEW for a couple weeks; please tell me if I'm using poor habits or doing anything incorrectly.
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Attachments:
IMU_serial_in.vi ‏61 KB

Hi Ryan,
I have a suggested methodology, but I don't currently have any example code to share that would get you started.
The challenge you have is even if you sample at the exact right baud rate of your incoming signal, the phase of the FPGA clock will not be exactly the same as the source signal. Now complicate that with your sample frequency and baud rate will always be slightly different, and you will get the sampling drift effect you described where data eventually is clocked in wrong. On short transmissions, this may not be a problem because the sampling can be re-aligned with a start bit, but for long, continuous streaming, it eventually fails as the sampling and source signals drift out of phase.
I would suggest over-sampling the DIO line, using a debounce filter if necessary, and use a measured time between edge detections to constantly adjust your sampling period and phase to keep your sampling aligned with the incoming data.
The proposed LabVIEW code I imagine would be a single-cycle timed loop based state-machine. Essentially the state machine could detect edges that occur near the baud rate you expect to receive, and then would adjust the sampling period to ensure you are sampling the data inbetween transitions while the incoming waveform is stable.
With this method running at 40MHz, you would essentially have ~43 clock ticks/samples of each clock cycle at 921.6kbps, and you should be able to pull out the right samples at the right time in the waveform.
Hope this helps, and if I find a good example of this, I'll send it your way.
Cheers,
Spex
National Instruments
To the pessimist, the glass is half empty; to the optimist, the glass is half full; to the engineer, the glass is twice as big as it needs to be...

Mapping asynchronous to a serial interface

Hello everybody,
i got an ISR3845 with PVDM2 inside. The goal is to map a incoming call depending on the caller number to a dedicated serial interface.
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Asynchronous serial com with DAQ6034E

Hello,
I am a new CVI programmer, and i would like to submit a problem.
I use a DAQ6034E card with LabWindows/CVI. I would like to communicate with devices via an asynchronous serial bus. Is it possible to do such a thing with a digital I/O, and how can I do (especially for reception) ?
Thank's for your help !
Franck...

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Architectural Issues with AIA Asynchronous MEP

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I understand this is possible, but it seems an overkill to me when I could have two ports on the Provider ABCS wsdl (which the service constructor does not create), which I could then callback on and the EBS will then create a callback to the calling client. This would make the whole process easier to manage IMO.
I could change the generated WSDL and add a callback port, but as the service constructor generates the ABCS like this, I do not want to just alter this without understanding maybe why I shouldn't.
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Have people implemented the two port single WSDL solution (as is created by SOA Suite if you build a service as Async from scratch) as an AIA provider?
If anybody has a sample Async project in AIA showing this sort of scenario, I would love to see it.

Hello,
Provider ABCS does not need to have 2 port types for this scenario. You would have 2 port types in Provider ABCS only if it interacts with provider application in an asynchronous manner. In that situation, provider application will be sending the callback response by invoking the service operation defined in the callback response port type within provider ABCS.
Your question is more about why we need to have 2 EBS - one for processing request and another for processing callback response. For this situation, you do not have to add additional port type in provider ABCS WSDL.
You can certainly leverage the mediator’s call back facility to eliminate the Response EBS that is normally recommended for processing the callback. 11g mediator does have the support and you can leverage that.
We did look at this feature during the 11g adoption and decided not to leverage this feature after prototyping for the following reasons:
1.     EBS Operations need to support fire-and-forget as well as asynchronous delayed response MEPs. We had to support this functionality of Requester ABCS at run time indicating in the EBM whether it needs the response or not. EBS.Operation would be invoked by both fire-and-forget and asynchronous delayed response MEP requesters; and for the delayed responses, ResponseEBS.Operation would be used. Hardwiring the MEP at the EBS Operation level would lead us to create 2 operations – one for fire-and-forget and another for asynchronous delayed response
2.     This stateless programming model allows us to be OSB-friendly
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Any custom solution built by you can certainly leverage the 11g Mediator's callback facility provided your requester ABCS is coded always to receive a callback from EBS. You could certainly leverage this pattern if you dont have a need for Requester ABCS to invoke EBS using fire-and-forget pattern.
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Asynchronous serial message read

Hi, everybody.
I have the message based device. I don't know when the device will send the message, so I didn't know how should I create the VISA read function to read whole string from the device(because it reads only data, which are enabled at serial port buffer).May be it can be done by using VISA bytes at port in while loop, but I don't know exactly how.Can you explain it to me?Or do you have any other solution?Thank you for your help.
Solved!
Go to Solution.

Hi
I reworked the basic serial read and write example, just to give you some programming hint. Also remember that then reading from the serial buffer, you do not need to read all the content. Read the number of bytes you need. The serial buffer is FIFO type. So the oldest content will always be first in the queue to read.
My example is somewhat simple, and I did not test it but should work. Check out queues and notifiers (in example finder) for more advanced programming techniques.
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
Attachments:
Basic Serial Write and Read async.vi ‏33 KB

Asynchronous serial

It appears that when calling viReadAsync, it will not return until it times out or it receives at least as many bytes as I requested. Is there a way to make it return when it finds any data in the buffer? Currently, I am setting 'count' to 1, but this seems a bit inefficient.
Once viReadAsync and viWaitOnEvent have completed, I am having problems getting the number of bytes read. Is this always going to be the same number I requested? I tried using viGetAttribute to get VI_ATTR_RET_COUNT, but couldn't make that work. When I use the device session as the first arg, it returns VI_ERROR_NSUP_ATTR. When I use the job ID from viReadAsync or VI_EVENT_IO_COMPLETION, VI_ERROR_INV_OBJECT is returned. What is the secret to getting the number of bytes read?
Will viReadAsync ever return more bytes than I requested? What do I need to do to get all bytes in the input buffer? Do I need to check the number of bytes in the buffer, then request that many? How do I do this (I can't find that function/attribute)?

Are you using CVI? This is the LabVIEW forum. I can tell you though, that you can be use the VI_ATTR_ASRL_AVAIL_NUM to determine how many bytes are actually in the buffer and only do a read if the byte count is greater than 0. You will never get more bytes than what you request but you can get less. You will get less if you have the termination character enabled and the data includes the character. A VISA read will then terminate when the term character is detected, no matter how many bytes you specify.

Serial asynchronous architecture

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