Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Expansion Bus
Controller
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
664
Order Number: 306262-004US
12.4.1.7
Special Design Knowledge for Using HPI mode
The Expansion bus controller supports a number of the 8-bit and 16-bit versions of the
Texas Instruments Host Port Interface* (HPI) standards. This flexibility allows the
TMS320C54xx family of Digital Signals Processors (DSP) to seamlessly interface to the
Expansion Bus for the IXP45X/IXP46X network processors.
If the Expansion Bus CS (Chip-Select) is configured to operate to operate in HPI-8
Mode, then a STRH (16-bit write) Intel XScale processor instruction must be used for
writing to the HPI-8 device, even though it is in an 8-bit device. If a STRB (8-bit write)
instruction is used instead, then the Intel XScale processor’s data abort handler will be
initiated, causing the assigned HPI-8 CS signal to deassert.
However, there are some special things to note when using the Expansion Bus in HPI
mode of operation. These features are shown in the following tables. There are also
some restrictions on the timing parameters and these are outlined in
“Expansion Bus Interface Configuration” on page 658
The expansion bus address-pins bits 0, 1, 2, 22, and 23 are multiplexed with special
function signal pins for HPI as shown in
.
The byte identification signal, EX_HBIL, is used to determine the byte transfer order.
(EX_HBIL is driven low for the first byte of the transfer and driven high for the second
byte.)
The byte order bit (BOB) in the HPIC register (contained in the DSP) — within the HPI
device — is used to determine the placement for the two bytes of the transfer. Please
consult the datasheet of the specific DSP being connected to determine the order of the
transferred bytes.
When operating in HPI mode, bits 13:10 in the Timing and Control (EXP_TIMING_CS)
Registers are ignored.
When operating in HPI-16, non-multiplexed mode, the Expansion bus address bus
provides direct accesses to the DSP memory space. The data associated with this
address will be read or written from the location specified by the value contained on the
Expansion Bus address bits.
The signals EX_HCNTL [1:0] are multiplexed onto the EX_ADDR [2:1] pins. When
communicating to a multiplexed HPI interface, the EX_HCNTL [1:0] signals are used to
select one of four internal registers used for interfacing to the DSP. The EX_HCNTL
[1:0] mapping is described in the
.
Table 221.
Multiplexed Output Pins for HPI Operation
HPI Control Signal
Output Signal Pin
EX_HBIL
EX_ADDR [0]
EX_HCNTL [1:0]
EX_ADDR [2:1]
EX_HCSEL [1:0]
EX_ADDR [23:22]