DAC Buffer Output


I am using iio.py to interface with the ADRV9009. I want to use this library to transmit samples and mirror the DAC Buffer Output behaviour of the iio-oscilloscope. I have set the tx device 'raw' attribute of altvoltage0, altvoltage1,  altvoltage2 and altvoltage3 to 0. I have enabled voltage0, voltage1, voltage2 and voltage 3 of the tx device. I have also created a cyclic buffer within the tx device. However, I haven't written anything to the buffer and I get a tone. Any suggestions?