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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—HSS Coprocessor
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
726
Reference Number: 004US
• Ten FIFOs per HSS core, 5 for TX, 5 for RX (1 voice, 4 HDLC).
• The four HDLC FIFOs can be programmed to operate as either 2 FIFOs or 1 FIFO.
• Two lookup tables are employed per HSS core (1 for TX, the other for RX), this
allows voice/HDLC channelization, also removes unassigned timeslots.
• Condition signals are used to indicate the status of the FIFOs with the HSS.
• An ATM-TC scrambler and HEC generator are supplied within the HSS.
• The line clock speed is programmable (allowing differing protocols speeds).
• Loopback facility available for debug purposes.
• Very flexible frame generation options (allows HSS to interface to many framers),
the following are the programmable options,
— The frame pulse can be set active low, active high, falling edge or rising edge.
— The frame pulse and sync clock can be set as an input or an output.
— The sync clock can be can be set to positive or negative edge with respect to
(w.r.t.) the data.
— The sync clock can be set to positive edge or negative edge with respect to the
frame pulse.
— The data polarity can be set low or high.
— The data endianness can be programmed (w.r.t. what’s transmitted or received
first).
— Open drain mode on the tx data pins.
— The clock can run at the data rate or double the data rate.
— The output data can be high impedance, high or low when not driving data.
— The NPE Core can select to use FBit or not.
— The frame size can be programmed; the maximum value is 1,024 bits.
— The frame pulse offset can also be programmed; the maximum value is 1,023
bits.
— The NPE Core can detect if an unexpected frame pulse has been received (in
both TX and RX) by the HSS.
— The clock speed can run at 512 KHz, 1.536 MHz, 1.544 MHz, 1.568 MHz,
2.048 MHz, 4.096 MHz, 8.192 MHz depending on the protocol which is in use.
13.3
Theory of Operation
The external device communicates with the HSS coprocessor using three signals per
direction, namely a frame pulse, a clock, and data bit.
The data stream consists of frames, the number of frames depends on the protocol in
use. Each frame is composed of timeslots, each of these timeslots consists of 8 bits, the
number of the timeslot indicates its location within the frame, this timeslot count value
is maintained within each HSS core and the NPE Core has access to this information.
Some protocols use an FBit (frame bit) at the beginning of the frame (T1). In the case
where T1 is running at 1.544 MHz, the HSS will read in the received FBit, add on 7
padding bits (zeros in the 7 lsbs) and place the byte into the voice FIFO. The software
will read the FIFO location like any other timeslot. When MVIP is used where T1s are
located within the MVIP frame (see
), the HSS will not process the
FBits any differently to other timeslots, and will treat them as dictated by the lookup
tables (assign them as either voice/HDLC or unassigned).