Review13092010
1. Vadj plane should not be cut under SFP differential lines.
2. L2P Dframe, valid and clkp, should have 10K pull downs. These pulldowns drive the control signals to a known level when the FPGA is not driving them. There have been cases at the time FPGA is removed from reset that garbage data gets clocked into the fifo. This is not on the Gullwing 4124 ref design but it is present on the Altera GN4121 ref design. This is an important one to do.
3. Copied from spec review:
In the Gennum Gullwing reference design, pin E4 (PE_MODE) has a 4k7 pulldown and a jumper to 3V3. This pin has the function as described in Note 1 below.
- there is no trace of this functionality in the datasheet. I placed not mounted 0R resistor between E4 pin and P3V3. The reference design does have this same pulldown and switch for G6, D4, C4 (named OCT_EN0/1/2). I don't know the function and could quickly find it and asked Gennum now. In CERN's symbol it is marked as VSS...
- the same as in the datasheet
From a mail from Gennum:
_"We have a switch on SW6 (position 5) called PE_BODE (is suppose to
say PE Mode but someone must have had a cold that day!). That is for
forcing PCIe x1 or x4. In the off position it is x4 on it is x1. Most
systems that will force x1 mode when inserted in a x4 slot. This will
not change the resistive termination but will block any response on
lanes above lane 0.
There are some non compliant motherboards which only pay attention to
the receiver detect pulse only. At Power up the host sends a pulse on
the lane to do what is called receiver detect. It is a primitive TDR
method of determining presence of a receiver. In this case is a lane is
seen as present and doesn't respond the link should train down. Some
motherboards will think there is an error and shut of the slot entirely.
This is non PCIe compliant but we have seen some popular motherboards
have this issue._
In this case there are 2 solutions. Use a x4 to x1 adapter so there is
no mechanical connection of the add-in card fingers to the slot. Or
Simpler and cheaper, use masking tape on the edge connector to mask off
and make the card a masked x1 card. This applies not only to GN4124 but
to GN1406 as well."
Pablo 13/10/2010