prjxray/fuzzers/063-gtx-common-conf

GTXE2_COMMON Primitive Configuration fuzzer

This fuzzer is used to document the parameters corresponding to the GTXE2_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.