DMA transfer length problem

I still can not solve the problem.

I read the DMA control register and the length register .

The results of the two register are normal.

This is my soft program :

int main(void)

{

printf("Hello from Nios II!\n");

//perform the DMA test

unsigned int* data_source ;

data_source = (unsigned int*) alt_uncached_malloc(258624);

//fill the source memory

int m;

for(m=0 ; m < 258624 ; m++ )

{

*(data_source+m)=0x00111111;

}

//test the DMA

alt_dma_txchan tx;

tx = alt_dma_txchan_open("/dev/dma_0");

if(tx== NULL)

{

printf("\n DMA Test: DMA ERROR ");

}

// perform dma transfer

void* tx_data =(void*) data_source ;

int rc;

alt_dma_txchan_ioctl(tx,ALT_DMA_RX_STREAM_ON,(void *)(USER_DEFINED_ME_BASE));

if((rc=alt_dma_txchan_send(tx,tx_data, (1796*80*4) ,tx_done, NULL ))<0)

{

printf("\n Failed to post transmit request ,reason %i",rc);

exit(1);

}

printf("\n Wait for DMA Transfer ... ");

while(!tx_complete){}

printf("\n DMA Transaction complete ! ");

return 0;

}