PCI Express* Configuration Registers
792 Datasheet
19.1.53 PECR3—PCI Express* Configuration Register 3
(PCI Express*—D28:F0/F1/F2/F3/F4/F5/F6/F7)
Address Offset: ECh–EFh Attribute: R/W
Default Value: 00000000h Size: 32 bits
Bit Description
31:2 Reserved
1
Subtractive Decode Compatibility Device ID (SDCDID) — R/W.
0 = This function reports the device Device ID value assigned to the PCI Express
Root Ports listed in Section .
1 = This function reports a Device ID of 244Eh for desktop or 2448h for mobile.
If subtractive decode (SDE) is enabled, having this bit as '0' allows the function to
present a Device ID that is recognized by the OS.
0
Subtractive Decode Enable (SDE) — R/W.
0 = Subtractive decode is disabled this function and will only claim transactions
positively.
1 = This port will subtractively forward transactions across the PCIe link downstream
memory and IO transactions that are not positively claimed any internal device
or bridge.
Software must ensure that only one PCH device is enabled for Subtractive decode at
a time.
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