usart的初始化问题？

ftz666

在初始化中有这样一句
AT91F_PDC_Open((AT91PS_PDC) &(pUSART->US_RPR));

函数原型
//* \brief Open PDC: disable TX and RX reset transfer descriptors, re-enable RX and TX
//*----------------------------------------------------------------------------
__inline void AT91F_PDC_Open (

AT91PS_PDC
pPDC)


// \arg pointer to a PDC controller外设数据控制
{

//* Disable the RX and TX PDC transfer requests

AT91F_PDC_DisableRx(pPDC);

AT91F_PDC_DisableTx(pPDC);

//* Reset all Counter register Next buffer first

AT91F_PDC_SetNextTx(pPDC, (char *) 0, 0);

AT91F_PDC_SetNextRx(pPDC, (char *) 0, 0);

AT91F_PDC_SetTx(pPDC, (char *) 0, 0);

AT91F_PDC_SetRx(pPDC, (char *) 0, 0);


//* Enable the RX and TX PDC transfer requests

AT91F_PDC_EnableRx(pPDC);

AT91F_PDC_EnableTx(pPDC);
}
函数中给的参数(AT91PS_PDC) &(pUSART->US_RPR)怎么理解？