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AR# 39425

Virtex-6 GTH Transceiver - Byte and Bit ordering in Raw Mode

Description

When using the Virtex-6 GTH Transceiver in RAW mode, care needs to be taken to ensure that the data is received with the expected bit and byte ordering. This answer record describes how the received data will be presented to the RXDATA ports so that the user application can interpret it correctly.

Solution

For the MSB case
TX DATA[63:0] of
|
|FFFFFFFFFFFFFFFF
|FFFFFFFFFFFFFFFF
|0000000000000000
|0000000000000000
|
|results in RX DATA[63:0] of
|
|00000000F800FFFF
|0000000000000000
|FFFFFFFF07FF0000
|FFFFFFFFFFFFFFFF
|
[63:0]
FFFF FFFF FFFF FFFF


RED = First Bit received on the RX pins put on bit 15.
GREEN = Last Bit received on the RX pins put on bit 0.
[63:0]
0000 0000 F800 FFFF


RED = First Bit received on the RX pins put on bit 15.
GREEN = Last Bit received on the RX pins put on bit 0.
[63:0]
0000 0000 0000 0000


RED = First Bit received on the RX pins put on bit 15.
GREEN = Last Bit received on the RX pins put on bit 0.
[63:0]
FFFF FFFF 07FF 0000

RED = First Bit received on the RX pins put on bit 15.
GREEN = Last Bit received on the RX pins put on bit 0.
*Note about MSB mode: User needs to swap around [63:48] with [15:0] and [47:32] with [31:16].
Now for the LSB case.
TX DATA[63:0] of
|
|FFFFFFFFFFFFFFFF
|FFFFFFFFFFFFFFFF
|0000000000000000
|0000000000000000
|
|results in RX DATA[63:0] of
|
|00000000001FFFFF
|0000000000000000
|FFFFFFFFFFE00000
| FFFFFFFFFFFFFFFF
[63:0]
FFFF FFFF FFFF FFFF


GREEN = First Bit received on the RX pins put on bit 0.
RED = Last Bit received on the RX pins put on bit 15.
[63:0]
0000 0000 001F FFFF

!!!!!!!!!INSERTPICTURE!!!!!!!!!!
GREEN = First Bit received on the RX pins put on bit 0.
RED = Last Bit received on the RX pins put on bit 15.
[63:0]
0000 0000 0000 0000
!!!!!!!!!INSERTPICTURE!!!!!!!!!!
GREEN = First Bit received on the RX pins put on bit 0.
RED = Last Bit received on the RX pins put on bit 15.
[63:0]
FFFF FFFF FFE0 0000

Assuming the LSB/MSB attribute is set to MSB.
User wants bit 63 transmitted first on the TX pins, bit 0 transmitted last.
Bit 63 now contains the oldest bit while bit 0 contains the newest as they arrived on the RX pins.
GREEN = First Bit received on the RX pins put on bit 0.
RED = Last Bit received on the RX pins put on bit 15.
Byte Alignment using RXSLIP:
RXSLIP operates on the internal datapath.
For example,64-bit external fabric interface, 16-bit internal: 16 possible slip positions.
Forexample,80-bit external fabric interface, 20-bit internal: 20 possible slip positions.
Assuming 16-bit internal datapath width, if your comma was 16 bits, if you continue to slip, you would eventually find your comma in either [63:48], [47:32], [31:16] or [15:0]. If your comma was 8 bits, it could appear in [7:0], [15:8], [23:16], [31:24], [39:32], [47:33], [55:48], or [63:56].
User needs to register and reorder the bytes from RXDATA
AR# 39425
Date Created 01/08/2013
Last Updated 01/16/2013
Status Active
Type General Article
Devices
  • Virtex-6