//wait until SSC_CLK goes HIGH
while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)) {
if(BUTTON_PRESS() || (usb_poll_validate_length() )) {
//wait until SSC_CLK goes HIGH
while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)) {
if(BUTTON_PRESS() || (usb_poll_validate_length() )) {