C Code for ADC

1) Make sure you compile everything with -O3

2) Get rid of superfluous boolean variables, use break and return.

3) Use do { ... } while (...); to remove the test from the loop top

4) Don't use 'const int' - it is still likely to be a variable.

I would code the bottom of the loop as:

// wait done
nWaitCnt = nMaxWait;
for (;;) {
    Data16 = IORD(READ_ADC_BASE,0);      //Data16 = Wert des Kanals
            if (Data16 & DONE_FLAG)
        break;
    if (--nWaitCnt == 0)
        // All gone horribly wrong....
        return 0;
    }
    DigitalValue = Data16 & 0xFFF         // 12 bits
    // stop
    IOWR(READ_ADC_BASE, 0, 0);            //Kanal löschen
    return DigitalValue;                   //DigitalValue zurückgeben      

You may also want to use gcc's __builtin_expect() to force which code paths are inlined.