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I have a navigation module constantly sending data over the serial port on the MXP connector. When autonomousInit is called I try to flush the. Owning Palette: Serial VIs and Functions Requires: Base Development System Initializes the serial port specified by VISA resource name to the specified settings. Wire data to the VISA resource name input to determine the polymorphic instance to use or manually select the instance. Use the pull-down menu to select an instance of this VI.
Install libusb compat ubuntu phone. SolutionThis error occurs when you are trying to access a VISA session that is already in use.To close VISA sessions that are open:. and close them through a LabVIEW built example, or. Close and reopen LabVIEW to release all open VISA sessionsUse the 'VISA close' VI to end the specific VISA session when you are done using it within your code. If you do not close your VISA reference, the computer will continue to reserve that port until you close LabVIEW. When LabVIEW closes, it closes all open VISA sessions until they are reinitialized next time your LabVIEW code runs.To see a properly built example using 'VISA Close,' see the LabVIEW example 'GPIB with VISA functions' in the LabVIEW example finder.
I have two computers connected via a null modem cable. One is the received for my serial data (where my application runs), while the other is simulating a sensor I will eventually have to talk to. The sensor continuously broadcasts updated readings (so this is not a query-response situation, it's more like drinking from a firehose).
Each message from the sensor is about 20 bytes long, and the sensor wants to send around 500 messages per second (so we're around 10kBps here).The serial ports on both computers are set to 115200N81 (although slower speeds still exhibit the problem; see below).Here is the problem: Any significant use of the receiving computer (switching applications or even just clicking in the window's title bar causes the receiving computer to return a ' VISA Error - (0xBFFF006C): An overrun error occurred during transfer. A character was not read from the hardware before the next character arrived.' I have replicated the problem with both my laptop (USB-RS232 adapter) on the receiving end and with a desktop machine (old-school RS232 on the motherboard). This happens even with the simplest of serial read/write code (e.g. NI's examples).I was able to find a pretty good overview of the meaning of the error in this.
Basically, it looks to me like the speed of the data stream is overrunning the capacity of the UART in the receiving computer before Windows comes around to service the IRQ and move the data out of there. I have tried all of the suggestions on the NI page without success (switching to RTS/CTS handshaking seemed to help a little, but the error still occurred). Reducing the baud rate to 9600 (laptop receiver) helped quite a bit, but the error still occurs with moderate abuse of Windows.So I'm bringing my problem here. My questions are as follows:.
Is there any way to mitigate this in software? Given that the sensor is just broadcasting data freely, I can't tell it to just wait for me to catch up. Is this really normal, for the UART on a modern laptop (and a modern desktop) to overrun at only Ten Kilobytes Per Second???:headbang:. Where (probably) is the UART in the laptop system? Is it on the motherboard, or is it in the USB-RS232 adapter? I've consulted all the documentation I have for both, and I can't find a clear answer.
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Basically, it looks to me like the speed of the data stream is overrunning the capacity of the UART in the receiving computer before Windows comes around to service the IRQ and move the data out of there. I have tried all of the suggestions on the NI page without success (switching to RTS/CTS handshaking seemed to help a little, but the error still occurred). Reducing the baud rate to 9600 (laptop receiver) helped quite a bit, but the error still occurs with moderate abuse of Windows.So I'm bringing my problem here. My questions are as follows:.
Is there any way to mitigate this in software? Given that the sensor is just broadcasting data freely, I can't tell it to just wait for me to catch up. Is this really normal, for the UART on a modern laptop (and a modern desktop) to overrun at only Ten Kilobytes Per Second???:headbang:.
Where (probably) is the UART in the laptop system? Is it on the motherboard, or is it in the USB-RS232 adapter? I've consulted all the documentation I have for both, and I can't find a clear answer.20 Bytes at 500 Hz is indeed 10 KBps, but Serial transmission is normally lsited as Kbps (note small and large 'b'). This, your 10 kBps becomes 80kbps without adding stop bits, parity and so on. Adding a stop bit and a parity bit moves this to 100kbps.This should still be below your 112500 kbps serial speed, but maybe it's just too close to the theoretical limit.Can you slow down the tranmission to only 250Hz and see if the problem goes away? Edit: I see you tried this already.Perhaps it's a simple flow control problem?
Check a different com port. I have good experience with Exsys USB-RS-232 controllers (prolific Chipset). Cheap and fully-featured.Shane.
That's due to lack of breakouts for the cable and lack of a scope.What I can tell you that the handshaking definitely seems to be working, in the sense that the transmitter and the receiver each time out if the other isn't running. But I guess if there's a noise issue then the problem would be that the handshake hiccups every so often.Well if you can't look then poke.Put a good ground between the RTN lines of both ends.I have seen this issue (bad grounds) affect Laptops (because they are isolated from ground via the battery) and USB-Serial adapters.Another point:You are reading ALL of the bytes at the port every time and NOT just a subset, CORRECT?Ben.
How are you offloading the buffer? Is the front panel of the reader visible?I don't see any example code, but you might want to use VI Server to start a high priority VI in the background that just pulls data as fast as possible from the resource (VISA?) and and then use a queue to pass the data to your parsing/analysis code.The other idea might be to replace the USB-RS232 adapter with a Ethernet-RS232 device. Most laptops will have an Ethernet port and the Ethernet-RS232 adapters have a dedicated processor and memory that would help buffer the data. The OS buffer would be much larger than the few bytes that a UART has and would help alot. A link to the adapter I usually use, I'm pretty happy until now. I tried some Moxa (good reputation) but they bombed on me - on multiple occasions. They apparently don't support software flushing of their buffers!
64 Bytes of buffer. Really not much. I've tried to search for the 19Qi, but I've yet to find anything of use (like Specs).
Maybe it's missing the HW buffer.Thanks for the link. I've been reasonably happy with Keyspan over the years, but a USB-RS232 adapter is one of those things that sometimes you just need to pony up and buy the really good one, so you can stop worrying about it.
Perhaps it's time to step up and get a new one. Thanks for the link. I've been reasonably happy with Keyspan over the years, but a USB-RS232 adapter is one of those things that sometimes you just need to pony up and buy the really good one, so you can stop worrying about it.
Perhaps it's time to step up and get a new one.Yup, I'd have to agree with that one. I mentioned it because the Moxa series 'should' be really good, but I had some problems with them. They have since released a new line, so perhaps they work better, I dunno.If it would be of interest to you, I could try out a sample transmission on one of my adapters (Code?). I'd be interested as to how it holds up. I also have a MOXA unit available, so a comparison may be interesting.Shane.
From Keyspan.In short you need their high speed adapter, your Qi ain't designed to do what you want.regardsPeter'Over the years, Keyspan has made several adapters in the USA-19 line. The USA-19 line is defined as sb erial Adapters with 1 DB9 port (these characteristics make up the part number uSA-19). The following information outlines the difference between each variant of the USA-19 line:Product Name: USB PDA AdapterModel Numbers: USA-19, USA-19x, USA-19Q, USA-19Qi-The models in the USB PDA Adapter line (models USA-19, USA-19x, USA-19Q, USA-19Qi) were designed for connecting Palm Pilots, Wacom tablets, and other PDAs to Mac and Windows computers. These adapters only had enough serial capabilities to communicate with PDAs and graphics tablets and therefore using these adapters with serial devices that aren't PDAs or graphics tablets IS NOT RECOMMENDED (the USA-19HS is the recommended adapter for any serial device).'
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