UltraSPARC-T1 (Niagara) 2 systems PCI Express Interface Units (PIU) have built-in performance counters which can be dumped by using busstat. The output of the busstat -l command shows the following devices for such systems:
imu#
mmu#
peu#
bterr#
where # is an instance number.
The use of this built-in performance counter is intended mainly for Sun field service personnel.