The wrsmd device driver is a pseudo driver that presents a type II DLPI interface. The driver uses a Sun proprietary interface over the wrsm driver to provide IP-based communication over the WCI network.
Before using DLPI over a WCI network, you must first configure the wrsm controller on that network. See wrsmconf(1M) for more information. Each wrsmd device is associated with a wrsm controller with a matching id.
ELF kernel module
Writing Device Drivers