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<p class=MsoNormal>I am trying to add a new point-to-point communications device
to SIMH. I am using sockets as the underlying communications mechanism and the
routines in sim_sock.c in particular. The polled nature of SIMH seems to be
causing me some intermittent problems however.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Background: I use two separate connections for each device,
one for the device to send data, and one for it to receive data. This is because
I want each device to be the same, otherwise for each point-to-point pair I
would have to configure one to be passive and listen for connections and the
other to be active, and I cannot necessarily anticipate which one will need to
communicate first. Essentially I need full-duplex. This means each device is configured
with its own receive port and the port of the remote device to which it is
supposed to connect. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>On the receive side I have to poll for incoming connections because
I do not know if the remote machine is even running, so I cannot wait for an
incoming connection as this would block the whole virtual machine. On the
transmit side I have to poll for an outgoing connection for largely the same
reason.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The problem: Sometimes the software gets itself into a state
where the transmit side starts a connection and then gets a WSAENOTCONN, and at
the same time the receive side gets a WSAECONNRESET. I think this is because of
the non-blocking nature of the sockets, required because of the polled nature
of SIMH. What seems to be happening is that the transmit side starts a
connection, the receive side sees it but in that time the transmit side has
decided that the receiver is not going to connect so it closes the connection
and then the receive side sees it as disconnected.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The question: I am doing the development on Windows, and
there are several mechanisms I could use to allow for asynchronous notification
of an incoming connection. The problem is that I am not sure how portable these
are to other environments.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I have tried making the sim_connect_sock block instead, but
I think that when the receive side is not running this would cause a huge
slow-down on the sending virtual machine (while it waits for the connect to
fail); and at the moment sim_connect_sock also prints an error message (WSAECONNREFUSED)
for each failed connect poll as a result of the receive side not being present.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I am looking for suggestions for the best way to deal with
this.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Rob<o:p></o:p></p>
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