21.1.2 General operation
The slave devices connected to the peripheral bridge are modules which contain a
programming model of control and status registers. The system masters read and write
these registers through the peripheral bridge. The peripheral bridge performs a bus
protocol conversion of the master transactions and generates the following as inputs to
the peripherals:
• Module enables
• Module addresses
• Transfer attributes
• Byte enables
• Write data
The peripheral bridge selects and captures read data from the peripheral interface and
returns it to the crossbar switch.
The register maps of the peripherals are located on 4-KB boundaries. Each peripheral is
allocated one or more 4-KB block(s) of the memory map.
The AIPS-Lite module uses the accessed peripheral's data width to perform proper data
byte lane routing; bus decomposition (bus sizing) is performed when the access size is
larger than the peripheral's data width.
21.2 Functional description
The peripheral bridge functions as a bus protocol translator between the crossbar switch
and the slave peripheral bus.
The peripheral bridge manages all transactions destined for the attached slave devices and
generates select signals for modules on the peripheral bus by decoding accesses within
the attached address space.
By default, reads and writes on the crossbar side of the peripheral bridge take two data-
phase cycles. On the IPS side, accesses complete in one cycle. If wait states are inserted
by the slave peripheral, access time will be extended accordingly.
21.2.1 Access support
All combinations of access size and peripheral data port width are supported. An access
that is larger than the target peripheral's data width will be decomposed to multiple,
smaller accesses. Bus decomposition is terminated by a transfer error caused by an access
to an empty register area.
Functional description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
336 Freescale Semiconductor, Inc.
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