Connection Timed Out

[Yiping Li]

Hi,

 

We are using the modbus with RS485, connecting to Raspberry Pi 2. And we have used the library Libmodbus. But we are facing an issue:

 

When we start our program, we had a “Connection Timed Out” and the Bad File Descritptor.

 

What kind of problem can it be?

 

We need your help, thanks in advance.

Here is part of our code:

int read_registers(){

    int errMRR;

    int j;

    int nbReg, cptValue;

    int indexRegisterValues = 0;

    uint16_t tabRegister[2];

    for(j=0;j<deviceCfg[0].nbDevice;j++){

        if(!strcmp(deviceCfg[j].connected ,"Y")){

            usleep(20000);

            if (deviceCfg[j].deviceAddress!=currentDeviceAddress){

                modbus_close(ctx);

                currentDeviceAddress=deviceCfg[j].deviceAddress;

                modbus_set_slave(ctx, deviceCfg[j].deviceAddress);

                if (modbus_connect(ctx) == -1) {

                    fprintf(stderr, "Connexion failed: %s\n", modbus_strerror(errno));

                    modbus_free(ctx);

                    return -1;

                }

            }

            if (deviceCfg[j].registerAddressFormat == FORMAT32){

                nbReg=2;

            }

            else if (deviceCfg[j].registerAddressFormat == FORMAT16){

                nbReg=1;

            }

            errMRR = modbus_read_registers(ctx, (deviceCfg[j].registerAddress) - 1, nbReg, tabRegister);

            if(errMRR == -1){

                fprintf(stderr, "Modbus read register error : %s\n", modbus_strerror(errno));

                registerValues[indexRegisterValues] = -1;

                indexRegisterValues++;

            }else{

                if (deviceCfg[j].registerAddressFormat == FORMAT32) cptValue=tabRegister[0]*pow(2,16) + tabRegister[1];

                if (deviceCfg[j].registerAddressFormat == FORMAT16) cptValue=tabRegister[0];

                printf("cptValue = %d\n",cptValue);

                registerValues[indexRegisterValues]=cptValue;

                indexRegisterValues++;

            }

        }

    }

    printf("#communication : %d \n",nbCommunication);

    nbCommunication++;

}

[Mughil Arul]

Hi,

You havent initialized a modbus_t structure ie ctx. use modbus_new_rtu() / modbus_new_tcp() function to initilize the  modbus_t structure.