VSC8257/VSC8258 Evaluation Board
ENT-AN1280 VPPD-04670 ENT-AN1280 User Guide Revision 1.3
8
There are seven loopbacks available. Three of the loopbacks are host-side loopbacks. These include
loopback H2, loopback H3, and loopback H4. Loopback H2 is the shallow loopback located in the XAUI-
PHY block before the 8b/10b endec. The deeper loopback includes loopback H3 in the PCS block right
after the
64b/66b gearbox and loopback H4 at the WIS block after the framer.
The other three loopbacks are line-side loopbacks (that is, SFI in and looped back to SFI out). This
includes loopback L3, loopback L2C, loopback L2, and loopback L1. Loopback L3 is the loopback at the
PMA block while loopback L2 is the loopback right before the data hits the XGXS block. The deepest
loopback, L1, is the loopback after the 8b/10b endec. When using loopback L1 with an external 10G
tester, the entire chip is exercised with the exception of the XAUI input and output buffers.
The GUI allows the user to turn on host- and line-side loopbacks for 10G LAN and 1G LAN modes.
Checking the box enables the loopback while un-checking disables it.
5.5
BIST
The following image shows the BIST page.
Figure 7 • GUI BIST Page
The BIST page is not for PRBS BIST, but for packet-based BIST. There is a packet BIST engine on each
channel. The DA, SA, type, PTP time, packet length, IPG length, and the data could be configured. The
CFG, configuration register, and the data path registers are also programmable. The definition of CFG
register is listed in table
. The data path register is
Generator Configuration (GEN_CFG), Address: 4xE900
reserved for factory use. The current GUI only supports BIST sending data at PMA output and receiving
data from PMA input.
On the checker side, there are counters for the good packets, CRC error, fragmentation error, and local
fault.
The generator and checker can be individually enabled for each channel. The BIST on the right column is
a packet bist engine. When enabled, the DUT will be sending packetized PRB31 traffic out at PMA
output and receiving packetized traffic in at PMA input.
Note: After inputting the value to the corresponding box, make sure a return is hit, or the input value
may not take effect. Also, the settings may not reflect the updated values until the user exits this page
and then returns to it.
