Intel® IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
September 2006 DM
Order Number: 252480-006US 299
Expansion Bus Controller—Intel® IXP42X product line and IXC1100 control plane 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. Setting 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.
Split transfers are supported for all transfer types and controlled by setting bit 3 of the
Timing and Control (EXP_TIMING_CS) Register. Multi-word read transfers requested by
the South AHB might be split. Only one access at a time may be split.
These 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 South AHB. When split transfers are initiated, the Expansion Bus
Controller acknowledges the read request. The South 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 South AHB will b e signal ed that th e read dat a is in the FIFO and t he 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 South AHB.
Retries also are supported and used predominately when expansion-bus requests are
issued while a split transfer is in progress. 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. Setting bit 3 — of each Timing and Control
(EXP_TIMING_CS) Register — to logic 0 disables split transfers for accesses to the
corresponding chip select.
For Chip Select 0, split transfers are disabled after reset. This feature allows the boot
device to provide uninterrupted 32-bit data words to the Intel XScale processor.
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 set to logic 0, writes to a specified chip select region are
ignored. 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 [0:3]). 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 set to logic 0, the ready bit is set 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:
• T1 – Address Timing