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PCI Bus Controller
Freescale Semiconductor
22-35
number to select one of the IDSEL lines. If the bus number is not equal to its secondary bus, but is within
the range of buses subordinate to the bridge, the bridge claims and passes that access through as a Type 1
access.
Figure 22-39. PCI-to-PCI Bridge Determining Match to Secondary or Subordinate Bus
22.4.1.5.4
Address Decoding
For positive address decoding, an address hits when the address on the address bus matches an assigned
address range. Multiple devices on the same PCI bus may use positive address decoding, though no
overlap in the assigned address ranges can occur. The PCI controller only implements positive address
decoding.
For subtractive address decoding, an address hits when the address on the address bus does not match any
address range for any of the PCI devices on the bus. Only one device on a PCI bus may use subtractive
address decoding, and its use is optional.
22.4.2
Configuration Interface
The PCI bus protocol requires the implementation of a standardized set of registers for most devices on
the PCI bus. The PCI controller implements a Type 0 Configuration register set or header. These registers,
discussed in
Section 22.3.1, “PCI Type 0 Configuration Registers,”
are primarily intended to be read or
written by the PCI configuring master at initialization time through the PCI bus. The PCI controller
provides internal access to these registers through an internal bus interface. As with most of the PCI
controller registers, they are accessible by software in the address space at offsets. Internal accesses to the
Type 0 configuration header do not require PCI arbitration when they are accessed internally and are
allowed to execute regardless of whether any write data is posted in the PCI Controller.
If the PCI controller is the host device or configuring master, the internal bus interface configures the PCI
Controller. An external master would configure the PCI controller through the external PCI bus.
More information on the standard PCI configuration register is in the
PCI Local Bus Specification,
Revision 2.2
.
PCI
Bridge
PCI
Bridge
Secondary
Bus
Subordinate
Bus
Primary
Bus
ColdFire
Device 0.0
.
Device 1.0
Device 0.1
Device 1.1
Device 0.2
Device 1.2
Device 2.2
Device 3.2
Responds
to Type 0
Responds
to Type 0
Processor
Содержание MCF54455
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