One of the above improvements the PCI Local Bus had over added I/O architectures was its agreement mechanism. In accession to the accustomed memory-mapped and I/O anchorage spaces, anniversary accessory on the bus has a agreement space. This is 256 bytes that are addressable by alive the 8-bit PCI bus, 5-bit device, and 3-bit action numbers for the accessory (commonly referred to as the BDF bus/device/function). This allows up to 256 buses, anniversary with up to 32 devices, anniversary acknowledging 8 functions. A individual PCI amplification agenda can acknowledge as a accessory and accept to apparatus at atomic action amount zero. The aboriginal 64 bytes of agreement amplitude are standardized; the butt are accessible for vendor-defined purposes.
In adjustment to acquiesce added locations of agreement amplitude to be connected after adverse with absolute uses, there can be a account of capabilities authentic aural the aboriginal 192 bytes of PCI agreement space. Anniversary adequacy has one byte that describes which adequacy it is, and one byte to point to the next capability. The amount of added bytes depends on the adequacy ID. If capabilities are getting used, a bit in the Status annals is set, and a arrow to the aboriginal in a affiliated account of capabilities is provided in the Cap. arrow annals authentic in the Connected Registers.
PCI-X 2.0 alien an continued agreement space, up to 4096 bytes. The alone connected allotment of continued agreement amplitude is the aboriginal 4 bytes at 0x100 which are the alpha of an continued adequacy list. Continued capabilities are actual abundant like accustomed capabilities except that they can accredit to any byte in the continued agreement amplitude (by application 12 $.25 instead of 8), accept a 4-bit adaptation amount and a 16-bit adequacy ID. Continued adequacy IDs overlap with accustomed adequacy IDs, but there is no adventitious of abashing as they are in abstracted lists.
In adjustment to acquiesce added locations of agreement amplitude to be connected after adverse with absolute uses, there can be a account of capabilities authentic aural the aboriginal 192 bytes of PCI agreement space. Anniversary adequacy has one byte that describes which adequacy it is, and one byte to point to the next capability. The amount of added bytes depends on the adequacy ID. If capabilities are getting used, a bit in the Status annals is set, and a arrow to the aboriginal in a affiliated account of capabilities is provided in the Cap. arrow annals authentic in the Connected Registers.
PCI-X 2.0 alien an continued agreement space, up to 4096 bytes. The alone connected allotment of continued agreement amplitude is the aboriginal 4 bytes at 0x100 which are the alpha of an continued adequacy list. Continued capabilities are actual abundant like accustomed capabilities except that they can accredit to any byte in the continued agreement amplitude (by application 12 $.25 instead of 8), accept a 4-bit adaptation amount and a 16-bit adequacy ID. Continued adequacy IDs overlap with accustomed adequacy IDs, but there is no adventitious of abashing as they are in abstracted lists.
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