GTPE2_COMMON Primitive Configuration fuzzer¶
This fuzzer is used to document the parameters corresponding to the GTPE2_COMMON primitive.
It uses pre-built JSON containing a dictionary of parameters, each one with four attributes:
Type: one of Binary, Integer, String, Boolean.
Values: all possible values that this parameter can assume. In case of
BIN
types, the values list contains only the maximum value reachable.Digits: number of digits (or bits) required to use a parameter.
Encoding: This is present only for
INT
types of parameters. These reflect the actual encoding of the parameter value in the bit array.
E.g.:
{
"PLL0_REFCLK_DIV": {
"type": "INT",
"values": [1, 2],
"encoding": [16, 0],
"digits": 5
}
}
In addition, there exist wires and PIPs that allow the connections of the GTREFCLK
ports to clocks coming from the device fabric instead of the IBUFDS_GTE2
primitive.
In fact, if the clock comes from the device fabric, the physical GTGREFCLK[01]
port is used instead of the GTREFCLK[01]
one (even though the design’s primitive port is always GTREFCLK
).
In the User Guide (pg 27), it is stated that the GTGREFCLK[01]
port is used for “internal testing purposes”.
Using this port is highly discouraged to get the reference clock from the fabric, as the recommended way is to get the clock from an external source using the IBUFDS_GTE2
primitive.
Therefore, in addition to the parameters, IN_USE
and ZINV\INV
features, this fuzzer documents also the GTREFCLK[01]_USED
and BOTH_GTREFCLK[01]_USED
features.