DMA Interrupt not issued

Hello,

I'm using Avalon msgDMA controller to do the DMA data transfer between a Nallatech pcie385n FPGA board and another PCIe device. I used OpenCL and Ubuntu OS as the programming platform. Also I modified the Altera Linux PCIe driver to implement this. In my code, I found that after the DMA descriptor is sent, I cannot get the DMA interrupt (the irq_status is 0). This problem occurs only in one data transfer direction and when transferring data in the other direction, the DMA interrupt is generated. I don't know why and does anyone know how come about this?

Thanks!