alt_avalon_sgdma_construct_mem_to_mem_desc()

I have realize the 320*240pixels data transmition,which the number of data is much larger than 65535,the code is as below:

for(buffer_counter=0;buffer_counter<=1;buffer_counter++)

{

alt_u32 *write_addr = (alt_u32 *) (DDR_SDRAM_BASE+0xE000*buffer_counter);

alt_avalon_sgdma_construct_mem_to_mem_desc(

&desc[buffer_counter],

&desc[buffer_counter+1],

read_addr,

write_addr,

65530,

1,

0);

}

alt_avalon_sgdma_do_async_transfer();

(PS: buffer_counter is the type of "alt_u32")

//////////////////////////////////////////////////////////

there is a question I am not understand:

how to know the SGDMA transmition is over?

I use the "alt_avalon_sgdma_register_callback" ,then add the code below after "alt_avalon_sgdma_do_async_transfer();",but the software seems stall there,so I hope someone could give me some advise!~

while(tx_done == 0) {}

printf("The transmit SGDMA has completed\n");