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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Ethernet MACs
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
238
Order Number: 306262-004US
Once the received frame has passed the frame validity checks, the received frame will
be checked for integrity using the Frame-Check Sequence Algorithm called out in the
transmit-frame section. If the frame passes the Frame Check Sequence, the frame will
be forwarded on to the NPE via the remaining receive logic. If the frame fails the Frame
Check Sequence, the frame will be discarded along with purging all of the remaining
receive logic of the frames contents.
Padded bytes will be included in the calculation of the Receive Engine’s Frame Check
Sequence for frames that were transmitted and were smaller than the 64-byte
minimum frame size. A status flag will be sent to the NPE to inform the NPE what to do
with the received frame.
In addition to the above features, the xMII receive interface allows some features to be
used for test and debug. The transmit interface can be looped back to the receive
interface by setting bit 4 of Receive Control Register 1 (RXCTRL1) to logic 1. In loop-
back mode, the Receive Engine will receive all of the data sent by the Transmit Engine.
The loop-back feature allows software developers to develop their application code and
test the code before they start dealing with physical interface problems. Setting bit 0 of
Receive Control Register 1(RXCTRL1) to logic 1 enables the Receive Engine. This
feature allows all initialization of the product to occur prior to bring the receive
interface online. Bit 0 of Receive Control Register 2 (RXCTRL2) enables deferral
checking on the receive side. The IXP45X/IXP46X network processors do not use the
receive side deferral checking feature.
Bit 0 of Receive Control Register 2 (RXCTRL2) must be set to logic 0 for proper
operation. Failure to do so will result in unpredictable behavior.
Intel recommends that the register values described in this section be manipulated
through Intel-supplied APIs. Failure to use the Intel supplied APIs will result in
unpredictable results.
In order to operate the interface in SMII mode of operation, the ethernet registers will
be configured as if they are in MII mode of operation. Any setting produced in MII
mode of operation should translate to the same mode of operation when the interface
is configured to SMII mode of operation.
6.1.6
General Ethernet Coprocessor Configuration
The Ethernet coprocessor contains various other registers that are used to configure
the interface. Some of these registers are included due to the generic nature of the
Ethernet coprocessor. Other registers are added to allow greater flexibility in
configuration of the Ethernet coprocessor.
The Threshold for Internal Clock (THRESH_INTCLK) Register is used to determine the
frequency relationship between the xMII interface and the host processor that is used
to control the xMII interface. The value in the Threshold for Internal Clock
(THRESH_INTCLK) Register will be manipulated based upon the ratio of
PHY_CLK_SPEED/HOST_CLK_SPEED.
The physical interface clock speed will be divided by the host-side clock speed and then
rounded to the nearest whole number. The value from this calculation will be written to
the Threshold for Internal Clock (THRESH_INTCLK) Register. For the IXP45X/IXP46X
network processors, the value contained in the Threshold for Internal Clock
(THRESH_INTCLK) Register must always be set to hexadecimal 0x01. Failure to do so
will result in unpredictable behavior. The value of the Threshold for Internal Clock
(THRESH_INTCLK) Register will be pre-programmed by the Intel-supplied APIs to the
proper value. Manipulation of this value will result in unpredictable behavior.