Type 0 Configuration Request

A configuration read or write takes the form of a Type 0 configuration read or write when it arrives on the destination bus. On discerning that it is a Type 0 configuration operation:

The devices on the bus decode the header's Device Number field to determine which of them is the target device.
The selected device decodes the header's Function Number field to determine the selected function within the device.
The selected function uses the concatenated Extended Register Number and Register Number fields to select the target dword in the function's configuration space.
Finally, the function uses the First Dword Byte Enable field to select the byte(s) to be read or written within the selected dword.

Figure 20-5 and Figure 20-6 illustrate the Type 0 configuration read and write request header formats. In both cases, the Type field = 00100, while the state of the Fmt field's msb indicates whether it's a read or a write.

Figure 20-5. Type 0 Configuration Read Request Packet Header

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Figure 20-6. Type 0 Configuration Write Request Packet Header

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[ Team LiB ]