Converts 10-bit data clocked at 125 MHz to 4-bits data clocked at 312.5 MHz. This 4-bit parallel data is then presented to OSERDES which converts it into serial stream of 1.25 Gbps.
The following file describes the gearbox 10 to 4 bit logic:
<project_dir>/<project_name>/<project_name>.srcs/sources1/ip/<component_name>/synth/sgmii_lvds_transceiver/<component_name>_gearbox_10_to_4.v