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PCI Bus Controller
22-42
Freescale Semiconductor
22.4.3.5
Transaction Termination
If the PCI cycle master aborts, interface returns 0xFFFF_FFFF as read data, but completes without error.
It issues an interrupt to the internal interrupt controller if enabled.
For abnormal transaction termination during an internal bus-initiated transaction (unsupported transfer
types, retry limit reached, or target abort) or if the crossbar switch transaction does not hit in the
PCI-defined space, an error (bus error reported in the SCMISR, see
Chapter 14, “System Control Module
,” for more information) generates. It issues an interrupt to the processor’s interrupt controller if
such interrupts are enabled.
Internal bus burst transfers to a PCI non-memory address range result in a transfer error (bus error reported
in the SCMISR). The space is non-memory if the IO/M# configuration bit associated with that window
clears. This type of unsupported transfer does not cause a PCI interrupt, but can trigger an interrupt from
the SCM.
22.4.4
Internal Bus Target Interface
This section discusses the PCI controller as a PCI target, and as such, the following apply:
•
The target interface can issue target abort, target retry, and target disconnect terminations.
•
The target interface supports fast back-to-back cycles.
•
No support of dual address cycles as a PCI target.
•
The processor does not snoop target transactions.
•
Medium device selection timing only.
•
Six 16-byte buffers enhance data throughput.
The internal bus target interface provides access for external PCI masters to as many as six windows of
internal processor address space. The PCIBATR0–5 registers allow the user to map PCI address hits on the
PCI controller’s base address registers (PCIBAR
n
) to areas in the internal address space. At least one of
these registers must be enabled for this interface to operate.
Upon detection of a PCI address phase, the PCI controller decodes the address and bus command to
determine if transaction is for local memory (BAR hit). If transaction falls within the device’s PCI space
(memory only), PCI controller target interface asserts PCI_DEVSEL, latches the address, decodes the PCI
bus command, and forwards them to the internal control unit as a privileged access. On writes, data
forwards along with the byte enables to the internal control unit. On reads, four bytes of data are provided
to the PCI bus and the byte enables determine which byte lanes contain meaningful data. If no byte enables
asserts, PCI controller completes a read access with valid data and completes a write access by discarding
the data internally. All other target memory transactions translate into internal bus master transactions.
There are address translation registers for each unique PCIBAR
n
register initialized before data transfer
can begin. These address registers correspond to BAR0–5 in PCI Type 00h configuration space register
Table 22-31. Unsupported Internal Bus Transfers
Internal Bus Transaction
PCI Address Space
Burst (16-byte)
Non-memory
Содержание MCF54455
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