Hello, i have implemented TCP IP Modbus communication protocol on Freescale ColdFire micro controller. The TCP IP stack is similar to windows TCP IP stack. For the moment it has just the server part of the protocol this means that other devices can connect to it. My problem is that i don't know how to maintain the connection, because it drops after a while. I had in mind, to use interrupts, but i don't know if this is the right solution. My database has around 2000 modbus signals ... Do you guys have any solution to this problem ? thanks and best regards. BoSCHoW.
Also when I was observing the communication with ethreal I found out this: - the client send a TCP IP packet SYN - then the servers responds with SYN ACK - and then the client sends ACK - and the client immediately sends a Modbus Query - the server sends Modbus respond - and then immediatly another package that is labeled TCP DUP ACK "11#1" - and then the sequence is repeated P.S. Sometimes the server also sends TCP Window size changed ... I think the problem is on the server side. I don't use any functions to close the connection. I just use SocketListen, SocketRecieve and SocketSend. I also should check if the server changed the port to keep the connection active ?? Best Regards, BoSCHoW.
Bostjan Gojkovic wrote: > Also when I was observing the communication with ethreal I found out > this: > - the client send a TCP IP packet SYN > - then the servers responds with SYN ACK > - and then the client sends ACK > - and the client immediately sends a Modbus Query > - the server sends Modbus respond > - and then immediatly another package that is labeled TCP DUP ACK "11#1" > - and then the sequence is repeated > P.S. Sometimes the server also sends TCP Window size changed ... > > I think the problem is on the server side. I don't use any functions to > close the connection. I just use SocketListen, SocketRecieve and > SocketSend. I also should check if the server changed the port to keep > the connection active ?? > > Best Regards, > BoSCHoW. Hi Gojkovicu. Can I speak to you on Serbian? It will be easier!:) I haven't much expirience with microcontrollers as I have with protocols. But, > - the client send a TCP IP packet SYN > - then the servers responds with SYN ACK > - and then the client sends ACK This means that client checking is server avalible and the server respond that he is. From next point, you can try to find a problem. > - and the client immediately sends a Modbus Query > - the server sends Modbus respond. Here can be an error if client overrun time about the server "reply time-out". In that case, server may open new Modbus deal, but reply will fail, because client cannont see that new one. But this: > - and then immediatly another package that is labeled TCP DUP ACK "11#1" > - and then the sequence is repeated > P.S. Sometimes the server also sends TCP Window size changed ... This is normal, because the server have to inform client about free space (memory) on his (server) side. And the size of that free space iz changing. TCP DUP ACK "11#1" is right that about size window. How much can client send to server. Try to find out how much is "11#1", because if server "talking" about the same size, there can be problem. I repeat CAN BE. Try to focus on that. Best wishes, Ili pozdrav:) Miroslav K.
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