# K1426–K1430 PCI header discovery contract

The first configuration DWORD supplies vendor and device IDs. The DWORD at
offset `0x0c` supplies the header-type byte in bits 16–23. A vendor ID of
`0xffff` means no usable function: discovery returns `Absent` before any
driver binding or inventory entry is published. Layout values 0, 1, and 2
identify endpoint, bridge, and CardBus headers; other values are rejected.

Function zero controls scanning scope for its device. With header bit 7 clear,
only function zero may be considered. With bit 7 set, functions zero through
seven may be considered. Each candidate still needs its own valid vendor ID.
The caller uses the checked ECAM address and keeps the Device mapping owned
while reading the two DWORDs. The logical inventory publishes a complete
identity only after all checks succeed; duplicate, absent, malformed, and
out-of-scope inputs preserve the prior inventory and resource count.

The positive local examples cover both single and multi-function headers.
The negative example supplies `0xffff` as vendor and checks that an existing
healthy identity remains available with no new binding. K1430 must measure a
real absent PCI function in a guest and verify that no driver is bound.