PYNQ: PYTHON PRODUCTIVITY

Vdma read error

Hi all,
I am writing camera data to the VDMA and i am reading back from VDMA while reading i am getting the fallowing error. what could be the problem ?

code
from pynq import Overlay
from pynq import Xlnk
import numpy as np
from pynq import allocate
import time
from PIL import Image
from pynq.lib.video import *
ol = Overlay("/home/xilinx/pynq/overlays/vdma/vdma.bit")
vdma = ol.axi_vdma_0
framemode= VideoMode(4096,1,24)
vdma.writechannel.mode = framemode
vdma.readchannel.mode = framemode
vdma.readchannel.start()
vdma.writechannel.start()
frame = vdma.readchannel.readframe()
print(frame)

Error

AttributeError Traceback (most recent call last)
in ()
----> 1 frame = vdma.readchannel.readframe()
2 print(frame)

/usr/local/lib/python3.6/dist-packages/pynq/lib/video/dma.py in readframe(self)
199 loop = asyncio.get_event_loop()
200 loop.run_until_complete(
→ 201 asyncio.ensure_future(self._interrupt.wait()))
202 pass
203 self._mmio.write(0x34, 0x1000)

AttributeError: ‘NoneType’ object has no attribute ‘wait’

Regards,
Gireesha