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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
730
Reference Number: 004US
13.3.2
Endianness
The endianness of the data bus must be taken into account when writing data to the
HSS for transmitting. The same goes for reading back received data.
Changing the endianness only affects data to/from the FIFOs within the HSS, writes to
the lookup tables are not affected.
When an 8-bit read is performed, the byte read will always be the byte received first.
The same principle applies to TX data written to the HSS by the NPE Core.
13.3.3
Programmable Frame Pulse Offset and Frame Synchronization
An offset can be programmed by the NPE Core between the frame pulse and the start
of the frame.
Before the HSS indicates to the NPE Core that it has received data, it must
synchronizes to the frame pulse.
The HSS must detect two frame pulses (in the case of gapped frame pulses, then on
the correct detection of the second frame pulse) to gain sync. RX frame pulses before
must be synchronized before any data is placed into the Rx FIFOs.
If there is no Rx offset (programmed value of 0), then the data at the start of the
second frame will be considered valid data and will be placed into the appropriate FIFOs
(lut dependent). If there is an offset programmed, then the first data at the beginning
of the third frame will be considered as the start of valid data. Either way, the first data
the NPE Core receives will begin at the start of a frame. Therefore, no timeslot counters
are needed within the HSS.
Figure 167. HSS Endianness Examples
B4235-01
31
0
29
27
25
21
19
17
15
13
11
9
7
5
3
1
30
28
26
24
20
18
16
14
12
10
8
6
4
2
0 = Tx/Rx first
31 = Tx/Rx last
when HSSTXPCR.Bit-end = 0
0
31
bus bit number
23 22
8 bit accesses between the NPE and the HSS
32 bit writes/reads of TX/RX between the NPE and the HSS
0
7
5
3
1
6
4
2
31
24
bus bit number
0 = Tx/Rx first
7 = Tx/Rx last
when HSSTXPCR.Bit-end = 0
24
7
26
28
30
18
20
22
8
10
12
14
0
2
4
6
25
27
29
31
19
21
23
9
11
13
15
1
3
6
0 = Tx/Rx first
31 = Tx/Rx last
when HSSTXPCR.Bit-end = 1
0
31
bus bit number
16 17