translate 320*240 pixels though DMA in sopc

hi: gurus

I write a custom component using quartusII megecore FIFO which attach to Avalon bus,I use this custom component to translate 320*240 data to the sdram by DMA,now I can translate 1024 pixels ,and the waves in signaltapII and the data saved in sdram are both right , but when I change the 1024 to 2048 or more,then the software seems to be stop ,and says that "..not suspend "or something,then I try to change the DMA setting :using the burst mode ,and it donnot paly a part too.

so ,is there somebody tell me what is the reason,if or not the FIFO can not translate so much datas(320*240)??

thanks for your help~

best regards