A device for controlling data communication flow to a data buffer of an integrated circuit is disclosed. The device receives data communicated from a transmitting device. The received data is placed in a data buffer in memory. The data buffer is defined by a set of buffer descriptors, whereby a number of free buffer descriptors in the set of buffer descriptors is indicative of the amount of free space in the data buffer. A communications controller determines whether the data buffer is subject to overflowing by determining when the number of free buffer descriptors moves below a threshold level (a watermark). The communications controller sends a request to the transmitting device to stop transmitting data in response to determining that the data buffer is possibly subject to an overflow condition, indicating that the data buffer is nearly full.