am3359 mcasp send problem

i use mcasp to send data from arm3359 to fpga, i use EDMA to transfer data.

the data was not continuous.   i send a packets and after some send another, but i find 

when i configure my EDMA parame like this :

static struct EDMA3CCPaRAMEntry const txDefaultPar = 
       {
           (unsigned int)(OPT_FIFO_WIDTH), /* Opt field */
           (unsigned int)loopBuf, /* source address */
           (unsigned short)(BYTES_PER_SAMPLE), /* aCnt */
           (unsigned short)(NUM_SAMPLES_LOOP_BUF), /* bCnt */ 
           (unsigned int) SOC_MCASP_1_DATA_REGS, /* dest address */
           (short) (BYTES_PER_SAMPLE), /* source bIdx */
           (short)(0), /* dest bIdx */
           (unsigned short)(oxffff), /* link address */
           (unsigned short)(0), /* bCnt reload value */
           (short)(0), /* source cIdx */
           (short)(0), /* dest cIdx */
           (unsigned short)1 /* cCnt */
       };

my EDMA link address is NULL.

i can send the first packet , i can not send the next packet , the mcasp can not work.

so i wonder if data send by the mcasp must be continus?  

i have tried TDM mode and Burst mode, neither is working.