CODEWITHSUNDEEP
cvariablespointersglobal
ritchie888
ritchie888

Reputation: 583

Passing pointer address to global variable

I have a pointer which is being passed into a function like so:

unsigned char globalvar;

int functionexp(unsigned char *buff){
    globalvar = buff;
    //start interrupt
    //wait for end of interrupt
    //pass original pointer back with updated results
}

void __attribute__((interrupt, no_auto_psv)) _DMA2Interrupt(void) {
    globalvar = somedata;
}

And I have an interrupt which collects data that I need to pass into said pointer. What I want to do is create a global dummy variable and copy the original pointer (bufF) address into this global variable, so when I write data to the global variable which I can access within the interrupt (as I can't pass the original pointer into the interrupt) it also updates the values in the original pointer.

My example shows the basis of what I want to do, but without the pointer syntax. Could someone please show me how to do this, please!

Upvotes: 0

Views: 820

Answers (1)

Rhialto supports Monica
Rhialto supports Monica

Reputation: 456

Your question isn't entirely clear. My first interpretation of what I thought you're trying to do, it would be something like this:

unsigned char **buffptr;

int functionexp(unsigned char *buff){
    buffptr = &buff;
    //start interrupt
    //wait for end of interrupt
    //pass original pointer back with updated results
    // after this point, the value of buffptr is completely useless,
    // since buff doesn't exist any more!
}

void __attribute__((interrupt, no_auto_psv)) _DMA2Interrupt(void) {
    *buffptr = somedata;  
    // this changes the 'buff' variable in functionexp
}

On the other hand you could simply mean this:

unsigned char *globalbuff;

int functionexp(unsigned char *buff){
    globalbuff = buff;
    //start interrupt
    //wait for end of interrupt
    //pass original pointer back with updated results
}

void __attribute__((interrupt, no_auto_psv)) _DMA2Interrupt(void) {
    globalbuff[0] = somedata;
    // this changes data inside the buffer pointed to by the 'buff' 
    // variable in functionexp
}

Upvotes: 2

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