Re: Thorny Serial Comms "UART: Overrun" error Windows CE 5.0
- From: "Chris Tacke, eMVP" <ctacke@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 5 Apr 2005 17:54:21 -0400
I'd try the handshaking. I did extensive testing on the library and found
speed to be comparable to a C implementation.
--
Chris Tacke
Co-founder
OpenNETCF.org
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"Andrew Revell" <andrew_revell@xxxxxxxxxxx> wrote in message
news:6dd1a40b.0504051257.3506a786@xxxxxxxxxxxxxxxxxxxxx
> OK. I will try to be more precise with my description.
>
> First of all, in my case I am actually looping back from one COM port
> on my WinCE device to the another (with a cross serial cable).
> Previously I was communicating with an external machine (which was
> when I noticed the problem). I have switched to looping back onto
> myself so I have more control of the comms.
>
> So the numbers I quoted are for the % of reads that do not succeed.
> That is, I output 1000 bytes on one port, then attempt to read these
> 1000 again on the other. 8% of the time at 19200, the full 1000 bytes
> are not read (say 998 are), and I get the CommErrorEventHandler event
> fired.
>
> I don't know if it is the serial driver or the UART. What actually
> happens is that within the OpenNETCF code, the
> "m_CommAPI.WaitCommEvent(hPort, ref eventFlags)" call fails, and when
> "m_CommAPI.ClearCommError(hPort, ref errorFlags, commStat)" is called,
> errorFlags has (only) the OVERRUN bit set. This code interprets this
> as a UART error.
>
> (This code can be found at
> http://www.opennetcf.org/SourceBrowse/view.aspx?f=d:/sites/OpenNETCF/InetPub/wwwroot/Source/OpenNETCF/IO/Serial/Port.cs
> - about line 913 - 1011)
>
> So I am at a bit of a loss...
> It doesn't appear to be related to how fast my app reads the data - I
> am basically going full speed in a tight loop. The buffers I am using
> (which get passed to "m_CommAPI.SetupComm(hPort, rxBufferSize,
> txBufferSize") are large - 10000 bytes.
>
> It would seem to me that the best approach at this point is to:
> a) Try and get hardware handshaking to work. The external device
> supports DTR/DSR)
> b) Rewrite in C (to bypass any problems with OpenNETCF/CF.NET?)
>
>
> pietdesomere@xxxxxxxxx (Piet) wrote in message
> news:<b498cce3.0504042314.1fc30326@xxxxxxxxxxxxxxxxxx>...
>> What do these percentages mean? Do you lose 8% of the bytes?
>>
>> Do you know if it's the UART's FIFO buffer or the Serial Driver's
>> buffer that overruns? Do you have debug output from the serial driver?
>>
>> If it's the UART's FIFO buffer: I think you should be fast enough to
>> read even at 115200, and if you are not handshaking should solve this.
>> You say it makes no difference, this could mean it's not enabled on
>> the other side. Can you change the settings for the thing you're
>> communicating with?
>>
>> If it's the Serial Driver's buffer that overruns, your application is
>> not reading fast enough. If you create a loop that does nothing except
>> reading from the COM port, and you read say 4K at a time, and you
>> still have problems the problem is probably not in your application.
>>
>> From your description it's most likely the UART buffer so I think you
>> will need handshaking.
>>
>> Regards,
>> Piet
>>
>> andrew_revell@xxxxxxxxxxx (Andrew Revell) wrote in message
>> news:<6dd1a40b.0504041731.3f59cd91@xxxxxxxxxxxxxxxxxx>...
>> > I am writing an application on the following platform:
>> >
>> > Advantech 133Mhz PCM3348.
>> > Windows CE 5.0 (Build 1400).
>> > Compact Framework
>> > OpenNETCF SDF 1.2.
>> >
>> > What I am experiencing is within my C# code, I am occasionally getting
>> > a UART: Overrun error (caught by the handler for
>> > CommErrorEventHandler).
>> >
>> > The pattern is roughly:
>> >
>> > 9600 baud ? no errors (or so few I never see them).
>> > 19200 baud ? errors about 8% of the time.
>> > 115200 baud ? errors about 11% of the time.
>> >
>> > Number of errors also increases as the number of received increases.
>> >
>> > Along with the CommErrorEventHandler event being fired, the received
>> > buffer is usually missing a char or two (out of 1000). The position of
>> > the missing char is random.
>> >
>> > Things that do not seem to make a difference:
>> > Handshaking (DSR/DTR, CTS/RTS etc)
>> > Buffer sizes (I have set to 10 times maximum receive buffer).
>> >
>> > I have also given the "Installable ISR" serial driver a go, by putting
>> > entries such as:
>> > "Irq"=dword:4
>> > "IsrDll"="isr16550.dll"
>> > "IsrHandler"="ISRHandler"
>> >
>> > This _appears_ to improve matters, but not fix completely.
>> >
>> > I have tried this with another .Net library as well (CFSerialClass).
>> > The number of errors are less, but not much.
>> >
>> > What I would appreciate advice on is:
>> >
>> > Is this a common problem when dealing with serial?
>> > Are these errors just a fact of life with serial? But surely 19200
>> > isn't too fast for it to handle?
>> > Should I try writing direct eVC++ code? Will this help?
>> > Are there settings in the Device Control Block that could help here?
>> > Should I try changing serial interrupt priorities? If so, how?
>> >
>> > I guess I am searching for ways of narrowing this down. Is it
>> > OpenNETCF, .NET, Windows CE, my hardware??.?
.
- References:
- Thorny Serial Comms "UART: Overrun" error Windows CE 5.0
- From: Andrew Revell
- Re: Thorny Serial Comms "UART: Overrun" error Windows CE 5.0
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- Re: Thorny Serial Comms "UART: Overrun" error Windows CE 5.0
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