In IDE i amble able to reach PMC regiters such as : PMC->PMC_PMC_PCR , PMC->PMC_PMC_SCER etc. I am trying to use programmable clock output on PCKx pins( if connected to ardunio board?) . I am writing to register PMC->PMC_PMC_SCER to enable prog. clock output. But I could not configure PCKx via PMC_PCKx registers IDE says ther is no such member. But in datasheed of atmel, there is. How can i reach those registers on ardunio IDE. Shall ? directly use the adress of the register or any other name is given to those registers ?

The PCK0,1,2 registers are arranged as an array, you should access them with:

  PMC->PMC_PCK[0] = ....;
  PMC->PMC_PCK[1] = ....;
  PMC->PMC_PCK[2] = ....;

you can find the PMC structure here: