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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
659
Expansion Bus Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network
Processors
Each chip select can be independently enabled or disabled by setting a value in bit 31 of
each Timing and Control (EXP_TIMING_CS) Register. Clearing bit 31 of the Timing and
Control (EXP_TIMING_CS) Register to logic 0 disables the corresponding chip select.
Setting bit 31 of the Timing and Control (EXP_TIMING_CS) Register to logic 1 enables
the corresponding chip select. Accesses to chip selects that are disabled result in an
AHB error response.
Split transfers are supported for all read transfer types and controlled by setting bit 3
(SPLT_EN) of the Timing and Control (EXP_TIMING_CS) Register. Setting bit 3 of each
Timing and Control (EXP_TIMING_CS) Register to logic 1 enables split transfers for
accesses to the corresponding chip select. Clearing bit 3 of each Timing and Control
(EXP_TIMING_CS) Register to logic 0 disables split transfers for accesses to the
corresponding chip select. Multi-word read transfers requested by the AHB might be
split. Only one access at a time may be split.
Split transfers require that the read data from the Expansion bus be stored in an eight-
word FIFO until all expansion bus transfers are complete before that data is forwarded
on the AHB. When split transfers are initiated, the Expansion bus controller
acknowledges the read request. The AHB will be relinquished until all the data is
acquired from the Expansion bus and stored in the eight-word FIFO contained in the
Expansion bus controller. After all of the data has been acquired by the Expansion bus
controller, the requesting master on the AHB will be signaled that the read data is in the
FIFO and the read transfer will complete — uninterrupted in its normal rotation in the
arbitration scheme. This feature allows for slow devices connected to the Expansion
bus not to impede the performance of data flow from high-speed peripherals (like PCI)
on the AHB.
Retries also are supported and used predominately when expansion bus requests are
issued while a split transfer is in progress. Retries may also occur when a write occurs
when a previous read or write is in progress. A split response will never occur during a
write transfer. The Expansion bus controller will never deassert AHB HREADY for writes;
the writes will be posted or retried. The Expansion bus controller will also retry reads
until all the words of the Expansion bus data transfer are in the data FIFO if SPLT_EN is
clear. The Expansion bus controller will not deassert AHB HREADY for reads.
Each chip select region has the ability to be write-protected by setting bit 1 of each
Timing and Control (EXP_TIMING_CS) Register. When bit 1 of Timing and Control
(EXP_TIMING_CS) Register is cleared to logic 0, writes to a specified chip select region
results in an error response. When bit 1 of Timing and Control (EXP_TIMING_CS)
Register is set to logic 1, writes are allowed to a specified chip select region. Chip select
0 will be write-protected after reset.
For chip selects 4 through 7 configured in HPI mode of operation, there is an associated
ready bit EX_RDY_N[3:0]. The ready bit is only used when the mode of operation is set
to Texas Instruments HPI mode. The ready bits are used to hold off the Intel XScale
processor when the given DSP is not ready to complete the transfer.
However, the polarity of this ready bit can vary based upon the DSP that is selected. Bit
5 of each Timing and Control (EXP_TIMING_CS) Register allows the polarity used by
each ready bit to be independently set. When bit 5 of the Timing and Control
(EXP_TIMING_CS) Register is cleared to logic 0, the ready bit is cleared to respond to
an active low signal (logic 0). When bit 5 of the Timing and Control (EXP_TIMING_CS)
Register is set to logic 1, the ready bit is set to respond to an active high signal (logic
1).
One final set of parameters that may be set prior to using Expansion Bus Interface Chip
Select 1 through Chip Select 8. After boot up, these parameters may be adjusted for
Chip Select 0 as well. These five parameters are the timing extension parameters for
each phase of an Expansion Bus access.
There are five phases to every Expansion Bus access: