Use the cmn_err(9F) function to print messages to a system log from within the device driver. The cmn_err(9F) function for kernel modules is similar to the printf(3C) function for applications. The cmn_err(9F) function provides additional format characters, such as the %b format to print device register bits. The cmn_err(9F) function writes messages to a system log. Use the tail(1) command to monitor these messages on /var/adm/messages.
% tail -f /var/adm/messages