problems about using Ethernet example in cyclone V GT development kits,help!!

I use the ethernet example which is in the cyclone V GT installation package( cycloneVGT_5cgtfd9ef35_fpga\examples\board_update_portal )

I download the c5gt_fpga_bup.sof into cyclone V GT Development board,and then debug my simple TSE driver ,I found some problem.

1: i set the TSE into loop mode, RX_SGDMA's ISR is printing the received loopback data.

the follow datas are received loopback data,i found a problem

in first RX interrupt ,the datas are correct, but in the follow RX interrupt ,the datas are always zero ??? why???

RX descriptor reported OK

0 0 ff ff ff ff ff ff 0 1c 23 17 4a cb 8 6 0 1 8 0 6 4 0 1 0 1c 23 17 4a cb c0 a8 1 2 0 0 0 0 0 0 c0 a8 1 72 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 0 0

RX descriptor reported OK

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

RX descriptor reported OK

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

RX descriptor reported OK

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

RX descriptor reported OK

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

RX descriptor reported OK

my simple drivers:

ethernet_init();

sgdma_tx_dev = alt_avalon_sgdma_open("/dev/sgdma_tx");

sgdma_rx_dev = alt_avalon_sgdma_open("/dev/sgdma_rx");

alt_avalon_sgdma_register_callback(

sgdma_rx_dev,

(alt_avalon_sgdma_callback) &sgdma_rx_isr,

//ALTERA_AVALON_SGDMA_CONTROL_IE_DESC_COMPLETED_MSK ｜

ALTERA_AVALON_SGDMA_CONTROL_IE_CHAIN_COMPLETED_MSK |

ALTERA_AVALON_SGDMA_CONTROL_IE_GLOBAL_MSK

,

0);

while(1){

usleep(1000000);

alt_avalon_sgdma_construct_stream_to_mem_desc(

&desc[10],//

&desc[11],//

rx_payload,//

0,//

0);//write_fixed

alt_avalon_sgdma_construct_mem_to_stream_desc(

&desc[2],

&desc[3],

buf,

66,

0,

1,//SOP

1,//EOP

0);

sgdma_rx和sgdma_tx

alt_avalon_sgdma_do_async_transfer(sgdma_rx_dev, &desc[10]);

usleep(100);

alt_avalon_sgdma_do_sync_transfer (sgdma_tx_dev, &desc[2]);

}

void sgdma_rx_isr(void * context, u_long intnum)

{

int i=0;

printf("RX descriptor reported OK\n");

for(i=0; i<68; i++){

printf("%x ",rx_payload);

rx_payload=0x00;

}

printf("\n");

}