I'm trying to read data from a MODBus/TCP controller and having some
issues with the timing of the read command. I request a block of
registers from the slave and it returns the requested bytes and header
just fine and very quickly. In order to read everything right, I have
to first read the first 6 bytes of the header to know how many bytes are
to follow. Once I know that, I do a read from socket tSock for <bytes>
characters. Note that ALL of the characters have been received in a
single packet so once I read the 6 bytes, the rest of the data is
already in the socket buffer.
The problem I have is when I do the second read, the read command blocks
for the socketTimeoutInterval before continuing. It doesn't matter what
I set it to, it will wait that long before continuing. I tried catching
the socketTimeout message but that message is never sent, even when I
set the socketTimeoutInterval to 5 milliseconds!
I am not using the read ... with message form of the command since I
want the handler to wait until all the bytes have been received before I
move on. Has anyone else seen this? Have I missed something in the
documentation or could this be something in the Windows code that
handles sockets?
Any help would be appreciated!
len morgan
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