I'm reading and writing the characteristics from my board using bluez-4.101. using gatttool.
sometimes i get Characteristic Write Request failed: or read failed.
Frequency of these errors is like 2/10, is there something that i can do to make full proof, if it is usual, I'd like to reduce the timeout i get before failing.
If you say the frequency is not 100% then this is probably not a software issue. Rather, you might have to bring that your devices are brought closer together so that there is less chance of interference, or that your advertising device has a higher tx power.
Unfortunately there is no option through the BlueZ commands to reduce the timeout. I'm guessing you are using the gatttool command to interrogate the gatt table on the other end. Use #gatttool --help-all for a full list of the options and you will see that the timeout is not one of them.
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At the moment I have a problem I cannot pin down. Seemingly at random my communication with my RS232 Alicat Device will get held up. It will get held up somewhere in the read or write process and be unable to complete it. Upon closing the VI I will get a "Resetting VI" error in Labview 2020. I am using 7 of the 9 RS232 ports. My question is:
How do I fix this problem so that I do not get a communication drop OR (more likely)
How do I code the system such that I can catch and move through this problem or reset the connection. Something of a VISA read/write timeout? Open to ideas on how to move past the block
Here is what I have gathered about the problem:
Windows 10, I’ve tested everything on multiple computers. It happens no matter what.
It happens at random. It might happen twice within 20 minutes or not for a couple of hours.
I have never experienced the error when probing the line. I don’t know if that is a clue, or if that speaks to the randomness of the problem
Baud Rate = 9600, Prior to this I was running at 19,200 and experienced equivalent issues. The manufacturer recommended lowering the baud rate to reduce noise. I have also isolated the cable from other parts of the hardware. At this point noise on the connection is not an issue, but I am still experiencing the error.
My buffer size is 1000 bytes.
By termination character is \r. I cannot imagine a scenario where it fails to read a termination character due to the size of my buffer
I'm querying it every 50ms. Far below the threshold of a standard timeout. Too much?
What I am currently testing.
Due to how my code block is setup I cannot yet confirm if it is getting locked up on the read or write block or both. I'm attempting to isolate the problem with only minor modifications to see if I can isolate it.
Attached is slimmed down version of my code that I isolated the error to.
I have experienced similar problems with some RS232 devices from different suppliers. The (quite bad) solution was to connect and disconnect for each communication command. The question would be what sample rate you need.
Another idea is to replace that device with an ethernet device. If I am not mistaken Alicat supplies those with Modbus (TCP).
The issue turned out to be specific to windows/my laptop. There is a USB setting that disables inactive USB's after a certain amount of time. The setting to disable the timeout was unavailable through the control panel on my laptop, though it was available on my coworkers. I had to use powershell commands to change the setting
I'm working with 2 little machines with limited unix tools. Both are conected between each other via serial. I'm transfering binary data, so the devices are on raw mode. The sending machine is sending files to the other one and between there's a delay of X ms (specified as parameter). I would like to know if it's possible to measure those delays on destination machine in order to identify how many files are coming. Till now i was using cat < /dev/ttyS5, but this is not a option to my purpose.
Any idea?
Thanks
IMHO the easiest way is to write a little program which is waiting for bytes on the serial line.
Everytime a character arrives some sort of timer/timestamp is reset.
Another thread could be evaluation this timer/timestamp in a loop and increment a counter if it's larger than a defined value.
But please be aware that you might experience delays from the serial line as there's the kernel and its scheduler "in between". Furthermore you'll need appropriate locking of course!
I am try to learn GSM network issues. I would like to know more about in detail "Trade-off between network overhead and call setup time". why network overhead will occurs and how it reflect on call setup time
Seems an odd question (I am guessing it from some course etc?).
All networks will have an overhead to set up a call, so maybe this is referring to the extra work required to 'find' the terminating mobile device.
This requires a query to the GSM 'database' associated with the terminating subscriber, the HLR (Home Loctaion Register).
Call setup is generally prioritised over other traffic, including paging in the terminating cell to tell the terminating device there is a call - other than that there is not a lot of specific overhead. IN high congestion situations the terminating cell may not be able to page the device which can mean the call cannot be set up - maybe this is what the question was referring to.
A bit of history: We have an application, which was originally written many years ago (1998 is the first date in PVCS but the app is about 5 years older than that as it originally was a DOS program). This application communicates with a piece of hardware via serial. When we got to Windows XP we started receiving reports of the app dying after a short time of running. It seems that the serial comms just 'died' and the app was left in a stuck state. The only way to recover from this situation was to restart the application.
The only information I can find regarding this problem was apparently the Windows Message system would miss that information was received, the buffer would fill and the system would get stuck. This snippet of information was left in a old word document, but there's no evidence to back this up. It also mentions that this is only prevalent at high baud rates (115200+).
The solution was to provide customers with USB->Serial converters along with the hardware.
Today: We are working on a new version of the hardware that will run across a network as well as serial ports. So to allow me to work on the network code, minus the actual hardware we are using a VSCOM NetCom113 device. It also installs a virtual comm port on the users (ie: mine) machine.
Now I have got the network code integrated with the app, it appears that the NetCom device exhibits the same behaviour as a physical commport. This is undesirable as I need the app to run longer than ~30 seconds.
Google turns up zero problems that we experience.
I was wondering:
Has anyone experienced this before? If so what did you do to fix/workaround the problem?
Does anyone have any suggestions as to whether the original author of the document is correct and what I can do to test the theory?
Unfortunately I can't post code as the serial code is tightly couple with the rest of the system, though if you have questions regarding it I can answer questions about it.
Updates:
The code is written using Win32 Comm routines - so I am using CreateFile, ReadFile. There's also judicious calls to GetOverlappedResult.
It's not hanging per se, it's just that the comms stops. You can access the menus, click the buttons, but nothing can interact with the connected hardware. Using realterm you can see that no data is coming in or going out.
I think the reference to the windows message is that the problem is internal to windows. Data has arrived but the kernal has missed it and thus not told the rest of the system about it.
Flow control is not used.
Writing a 'simple' test is difficult due the the fact that the code is tightly coupled and the underlying protocol is quite complex and would require a lot of work.
Are you using DOS-style serial code, or the Win32 CreateFile approach?
If the former, be very suspicious: if at all possible I'd convert to the latter.
If the latter, do you know on what kind of system call it's hanging? Are you in a blocking read call? or an overlapped I/O call? or waiting on an event? (I'm not sure I have enough experience to help, but those are the kinds of questions that come to mind)
You might also check into the queue size, which you can set with the SetupComm function.
I don't buy the "Windows Message system" stuff -- it sounds fishy; you can write good Win32 serial i/o code that never uses Windows messages.
edit: does your Overlapped I/O use events? I seem to remember something about auto-reset events occasionally missing their trigger... check your overlapped I/O calls very carefully to see whether you're handling the possible outcomes properly. Perhaps there's a way to make your code more robust by automatically cancelling the overlapped i/o and restarting another read. (I assume the problem is in the read half, not the write half?)
edit 2: A suggestion: assuming the win32 side has missed a byte or packet, and your devices are in deadlock because they're both expecting each other to respond to something, can you tweak the other side of the serial I/O to regularly send some type of "ping" packet with an incrementing counter? (and log the ping packets on the PC side; that way you can see whether you've missed any)
Are you sure you have your flow control set up correctly? DTR, RTS, etc...
-Adam
i have written apps that use usb / bluetooth serial ports and have never had an issue. with bluetooth i have seen bit rates (sustained) of 800,000 bps for long periods of time. most people don't properly implement the port.
My serial port
Not sure if this is a possibility for you, but if you could re-write the code using C#.NET you'd have access to the SerialPort class there. It might remedy your problem. I know a lot of legacy code based around the Win32 API for hardware I/O ports tended to fail in XP due to timing (had a small bit of experience with MIDI).
In addition, I don't know if you can use the Win32 method of Serial Port access in Vista, so that might shut out future MS OSes from being able to use your code.
I'm asked to read from and write to a half-duplex serial connection using POSIX calls (more specifically, writing in C on Linux 2.6.x). I'm having slight troubles finding detailed information on that particular model (most pages concentrate on full-duplex) and as I am getting slight anomalies when reading, I wanted to check whether maybe I am doing something wrong here.
With a half-duplex serial connection, I can only read or write. This is not a problem, as there is no unsolicited incoming data on the line - the only time any packages are sent to me (for reading) is when I asked for them beforehand.
So what my code does is to write() to the port whenever something needs to be sent. Should this data result in a response (something I know beforehand), I simply read(). There are no special functions I am calling - but maybe I should? And is this approach correct? I.e. write when the line is free?
I would read the Linux kernel source documentation, there may be a text file about the serial driver; if not, you could read through the actual driver code to see what it does (it's not as scary as it sounds, I promise!)