Unit API is a newer library designed by 4DSP to quickly identify the connected devices and the "units" of firmware blocks available through PCIe and TCP/IP and legacy ethernet connections.
All AXI-enabled firmware uses reference software that is 100% UnitAPI. For these reference software to interact with AXI firmware on Xilinx boards using the ethernet, a TCP/IP configuration on the host computer is often required.
The AXI firmware enables the Xilinx Boards (VC707, KC705, etc.) to use a static IP address at 192.168.1.10 and netmask of 255.255.255.0.
When an error of -50 is received by UnitAPI, this is a common message whenever the UnitAPI is unable to find the IP address that it is searching for to enumerate all of the firmware units in the design. The TCP/IP stack in the firmware you're using is configured for IP address 192.168.1.10.
Please double check that this is the IP address referenced in your DeviceConfig.xml file installed here:
C:\Program Files (x86)\4DSP\4FM Core Development Kit\Bins\Config\DeviceConfig.xml
In the XML tag: <TcpIp first_ip="192.168.1.10" last_ip="192.168.1.10" port="1000"/>
The user computer should connect to the Xilinix Board with a static IP address of 192.168.1.1 and netmask of 255.255.255.0. Once the axi firmware is loaded and ethernet connection established, the user can then ping the board to ensure it's connected - here is an example configuration: