How to create an environment variable in BSP startup file ?

QNX DEVELOPERS Realtime and Embedded
1

Hi everybody !

I want to create an environment variable in startup in order to retrieve it in a QNX program.
Startup will read the value in a EEPROM, store it in an environment variable and so my QNX program will retrieve it.

I saw that function add_typed_string can set predefined variable but I want to create a new one. The function add_string could be OK but how my QNX program can retrieve the index returned ?

Thanks for your help !

2

Metais,

Assuming you can read the EEPROM value at startup, how are you going to set the environment variable. Via a shell script or a C program?

From a shell script (or from the command prompt for testing) you can do the following:

export name=value

So for example you can do

export Metais=100

Then to see the value of Metais from a script/command prompt do

echo $Metais

which will then show 100.

To get the value of Metais from a C program you have the following code:

char *tmp = getenv(“Metais”);

This will load ‘100’ into the tmp string which you can then parse to get the value your looking for.

Note: You can use setenv() to set an environment variable from a C program if that’s what your using to read the EEPROM at start time.

Tim

3

metais,

Some terminology here. What you want to do is create a syspage entry (not an environment variable).

Creating a new property in the syspage is not difficult.

In order to oass some data from your startup to your application in a non-portable way, the easiest thing to do would be to use add_string() (rather than add_typed_string). Defining a string in the format of an environment variable make sense.

For example to add a property FOO with a value BAR:

(in the startup)

add_string("FOO=BAR");

To retrieve the property FOO at process time (QNX running)

char *p=SYSPAGE_ENTRY(strings)->data;

while(*p) {
   if(strncmp(p, "FOO", 3) == 0) {
     char buf[80];
     char *p1,*p2;

     // found property FOO, now copy string and strtok() on '=' to get value
     strcpy(buf, p);
     p1=strtok(buf, "=");
     p2=strtok(NULL, "");
    
     // p2 is equal to FOO value (in this case "BAR")    
     break;
   }
   p += strlen(p);
}

Since this is non-portable, you should be sure that the property is not something that maps into the CS stuff…

4

Tim,

BSP startup is written in C and setenv() function is not working at this moment.

Rgallen,

Your solution is working fine ! (the line p += strlen(p); should be p += (strlen(p)+1); because strings are zero terminated). I observed that size or syspage is 32768 bytes and that use bigger size then QNX is not started ! it doesn’t matter, I just need few bytes to transmit value.

Thanks you two for your answers.

5

It was typed on the fly as an illustrative fragment (I am surprised that was the only bug !).

Glad you got it working!

Rennie