4. Addressing > Legacy Mode
41
PEB383 User Manual
July 25, 2011
Integrated Device Technology, Inc.
Confidential - NDA Required
4.8
Legacy Mode
When the PEB383 is in Legacy mode it supports subtractive decode. This is a non-standard feature that
is enabled through the LEGACY bit in the
“PCI Miscellaneous Clock Straps Register”
When the PEB383 is in legacy mode, all MWr, MRd, IOWr, and IORd transactions received on the
upstream port (PCIe) that do not decode to an internal address are forwarded to the PCI Interface.
When the device is not in legacy mode, TLPs that do not fall between the base and limit registers are
handled as Unsupported Requests (UR).
When the LEGACY bit is set, the PROG field of
is changed to 0x1, indicating to
software that a subtractive bridge is present.
When the LEGACY bit is set all PCIe capabilities are hidden from software, and the following occurs:
1.
Next pointer in
“PCI Power Management Capability Register”
is set to 0, indicating it is the last
capability
2.
are treated as reserved
3.
“Advanced Error Reporting Capability Registers”
are treated as reserved
4.
Extended configuration registers are treated as reserved
Ti
p
When the PEB383 is configured in Legacy mode, the PCIe root port must also be configured
to support subtractive decode.