Re: An error occurred while using aSub to process Modbus data

[Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>]

Hi Feng,

I can see a few things differently from how I use aSub, I hope they can be of help. I will note them inline.

Cheers,

Érico

On 04/11/2024 05:55, LONG FENG via Tech-talk wrote:

Hi all,

I want to process Modbus format data, but it's not going very smoothly.

My record file content is as follows:  

record(waveform, "Sensor:waveform")
{
    field(DESC, "read data")
    field(DTYP, "stream")
    field(NELM, "40")
    field(FTVL, "UCHAR")
    field(INP, "@RS485Test.proto getData SI")
    field(SCAN, "5 second")
    field(FLNK, "ProcessSensorData")
}

I'm assuming you have made sure that Sensor:waveform is working correctly, and that ProcessSensorData is being processed as well.

record(aSub, "ProcessSensorData")
{
    field(INAM, "init_dose")
    field(SNAM, "dose")
    field(INPA, "Sensor:waveform NPP NMS")

Setting FTA and NOA here might also be useful.

    field(FTVE, "DOUBLE")

This field should be FTVA, no?

    field(OUTA, "Sensor:ai NPP NMS")

I normally use PP for output records.

    field(NOVA, "1")
}

record(ai, "Sensor:ai")
{
    field(DESC, "Dose Measurement")
    field(INP, "ProcessSensorData.VALA NPP NMS")

You don't need an INP field in this record, the ProcessSensorData record will write into it already.

    field(PREC, "3")
    field(EGU, "µSv/h")
    field(SCAN, "Passive")
}

dose.c:

#include <epicsExport.h>
#include <aSubRecord.h>
#include <registryFunction.h>

int init_dose(struct aSubRecord *psub) {
    double *p1 = (double *)psub->vala; 
    *p1 = 0; 
    return 0;
}

int dose(struct aSubRecord *psub) {
    char *inData;
    double *pout1, doseRate;
    unsigned char readData[4] = {0};

    inData = (char *)psub->a;

    pout1 = (double *)psub->vala;
    // For example, the returned data is: 01 04 0c 14 7b 3e 2e 00 03 00 00 00 00 00 00 ad c9. '14 7b' represents the low byte, and '3e 2e' represents the high byte.  
    readData[0] = inData[4];
    readData[1] = inData[3];
    readData[2] = inData[6];
    readData[3] = inData[5];

    doseRate = *((float*)readData);

C detail and probably not relevant for your issue, I don't think you can guarantee readData is correctly aligned for a float. A more portable implementation could use memcpy to copy readData into an intermediary float variable.

    *pout1 = doseRate;

You're not setting "psub->neva" to 1 here, to indicate that you wrote into one value of this array.

    return 0;
}

epicsRegisterFunction(init_dose); 
epicsRegisterFunction(dose); 

 

 I used caget to observe Sensor:ai, and the result is always:  

Sensor:ai                      2.20405e-38

I think I made a mistake in my processing function, so I wrote a simple test program as follows:

#include <epicsExport.h>

#include <aSubRecord.h>
#include <registryFunction.h>

int init_dose(struct aSubRecord *psub) {
    double *p1 = (double *)psub->vala; 
    *p1 = 0; 
    return 0;
}

int dose(struct aSubRecord *psub) {
    char *inData;
    double *pout1, doseRate;

    inData = (char *)psub->a;

    pout1 = (double *)psub->vala;
    doseRate = inData[3]*0.1;
    *pout1 = doseRate;

    return 0;
}

epicsRegisterFunction(init_dose); 
epicsRegisterFunction(dose); 

However, the result is always:  

Sensor:ai                      0

 

What should I modify? Please help me.  

Feng

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