Hi,

On CODESYS V3.5.19.50 I am using the latest 3S File Access library (CAA File & CAA Types) to save and retrieve configuration data from the User Data section of an SD card, via file called config.txt.

The application reads the file to memory once upon initialisation, and then the only other operation is overwriting the file with the updated configuration whenever the user changes the settings.

An issue is ocurring, seemingly randomly, where the config.txt file, and all surrounding directories, cannot be written to by the unit, returning a READ_ONLY_CAA error upon file open. This sometimes does not clear even after power-cycling the PLC several times, yet checking the file permissions with ls -l shows normal read, write, and execute access.

I am wondering if this is caused by the PLC itself or by an issue in my application. I have included my CAA File handler function block (SD_Card_Bin(FB).txt) and any associated types/calls below:

TYPE ConfigData :
STRUCT
    Config : ARRAY[0..256] OF STRING(64);
    NumberOfStrings : UDINT;
END_STRUCT
END_TYPE

TYPE Buffer :
    STRUCT
        Data       : ARRAY[0..SIZEOF(ConfigData)] OF BYTE;
        DataLength : UDINT;
    END_STRUCT
END_TYPE

A case within my MAIN PRG:

mode.WriteConfigDataToFile:
    VisuElems.CURRENTVISU := 'Screen_Write';
    IF xModeHasChanged THEN
        iErrorCount := 0;
        iRoute := 0;
    END_IF

    CASE iRoute OF
    0:
        inBuffer := ConfigData_To_Buffer(GVL.UnitData);
        xConfigError := FALSE;
        xDataConfigured := FALSE;
        iRoute := 1;
    1 : //Read Data from Card
        SD_Card_Bin.strFileName :=FileName;
        SD_Card_Bin.iFileOperation := 2;
        SD_Card_Bin(xExecute :=TRUE, WriteBuffer := inBuffer, xDone =>xDataConfigured, xError=>xConfigError, strErrorCodes=>strError);
        IF xDataConfigured THEN
            SD_Card_Bin(xExecute :=FALSE);
            IF xConfigError THEN
                iRoute := 32767;
            ELSE
                iRoute :=100;
            END_IF
        END_IF
    100: // The end
        bCurMode := mode.DisplayProcessVariables;
    32767: // Config error
        iErrorCount := iErrorCount + 1;
        IF iErrorCount > 2 THEN // Repeats 3 times, if no progress abandons and returns error
            bCurMode := mode.WriteError;
        ELSE
            iRoute := 0; // Try again
        END_IF
    END_CASE

I'd like to rule out my application as the cause of this bug - help via comments or criticism would be greatly appreciated.

In case of error while opening the file to read you assume that the file doesn't exist and try to create one. But it could be that the SD card is not ready yet or simply not there. I would try to check first if the SD card is there and accessible. Otherwise with FILE.Create you could end up creating a new directory that is not mapped to the SD card. This would explain the errors even after a reboot, though it doesn't explain the READ_ONLY_CAA error I guess? I would use FILE.DirOpen and FILE.DirList to check if the SD card is there and ready.