OpenBoot 3.x Command Reference Manual

Probing of Slots For PCI Busses

The Sun Ultra 250 UPA/PCI system has four PCI plug-in slots, distributed across a single PCI bus. Probing of slots for those busses is controlled by the following two NVRAM configuration variables:

Table G-1 NVRAM Configuration Variables

Variable Name 

Default Value 



3 ,2, 4, 5 

Controls probe order of plug-in devices under pcio



Controls skipping of PCI plug-in slots 

pci0-probe-list specifies the device probe order on the "B" bus of the 1F PCI Controller. Device 3 is the motherboard 876 UltraSCSI bus (internal disks), while devices 2, 4, and 5 are open 33MHz 32-bit slots for plug-in cards.

pci-slot-skip-list is a list (0 to 3) of PCI slots that should not be probed. The values "0" to "3" correspond to the backpanel PCI slots, from bottom to top.

The Ultra 250 systems provide 4 PCI plug-in slots, numbered from 0 to 3, bottom-to-top (accessible and labeled from the back of the system).:

Table G-2 PCI Plug-in Slots

PCI Slot 

PCI Bus PCI Device 






 32 bit

33 MHz 


 /pci@1f,4000/xxx@2 32 bit

33 MHz 


 /pci@1f,4000/xxx@4 32 bit

33 MHz  

 0pci0 /pci@1f,4000/xxx@5 32 bit


where the xxx will correspond to the particular PCI card plugged into that slot. For example, plugging an 875/glm SCSI controller card into slot 0 will yield /pci@1f,4000/scsi@5, while plugging an 876 dual-SCSI card into slot 3 will yield two separate "devices" /pci@1f,2000/scsi@1 and /pci@1f,2000/scsi@1,1.