The Solaris deadman feature was implemented for penetrating system hard hangs. It is enabled by default since Solaris 11 Update 1. The deadman mechanism checks the deadman timer status on all CPUs every second at interrupt level 14. In this situation, you can use the kernel debugger to diagnose the problem if kmdb(1) was loaded prior to the panic.
If your system hangs while the deadman feature is enabled, you should see output similar to the following example on your console:
panic[cpu1]/thread=30018dd6cc0: deadman: timed out after 9 seconds of clock inactivity panic: entering debugger (continue to save dump)
Inside the debugger, use the ::cpuinfo command to investigate why the clock interrupt was not able to fire and advance the system time.