Modbus_Receive Timeout

[Joe Wilcoxson]

I have a implementation of libmodbus acting as an RTU Server, the main loop looks like this:

while(runServer) {

uint8_t query[MODBUS_RTU_MAX_ADU_LENGTH];

rc = modbus_receive(mb, query);

if (rc != -1) {

modbus_reply(mb, query, rc, mm);

}

}

I use the runServer boolean to control when it needs to run, the only issue I am having is that when there is no client polling this server, the code stalls at modbus_receive(), therefore not checking while(runServer) and exiting the loop if needed. How could I put some sort of timeout on modbus_receive() so that if it doesn't get a query for a certain amount of time to go ahead and process the loop again and recheck while(runServer)?

[Stéphane Raimbault]

Hi Joe,

To do this you need to use select() syscall (on POSIX systems), you'll find an exemple in tests/bandwith-server-many-up.c

2013/5/10 Joe Wilcoxson <joe.wi...@gmail.com>

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[Joe Wilcoxson]

Stephane,

Thank you for the response, but after looking at the example and looking up select(), I'm still not exactly sure I understand what to do. Would you mind elaborating on exactly what select() is doing in this case?

Thank you 

[Stéphane Raimbault]

Joe,

I recommend you to read the select() documentation because it's not under the scope of libmodbus project (and it's not an easy topic).

http://man7.org/linux/man-pages/man2/select.2.html

2013/5/10 Joe Wilcoxson <joe.wi...@gmail.com>

[Bill Smith]

Stephane,
By what you wrote, am I to understand that the unit-test-server and client applications can not run as they are out-of-the-box for RTU without the same modification?

Thanks in advance for a reply,
Bill