Overview

The .io.json file produced by PnR is used by the Test Bench Generator to map input and output files to pads on the chip. Specifically, it describes a mapping from signal to pad, with metadata describing the signals mode ("in", "out", or "reset"), and the bit width.

JSON Schema

Eventually it would be great to turn this into a concrete schema which could be used to validate inputs and create a library for easily constructing these files.

{
    "<signal_name>": {
        "pad_bus" : "<pad_name>",
        "bits": {
            "<bit_index>": { "pad_bit":"<bit_index>" }
        },
        "mode": "<mode>",
        "width": <width>
    }
}

Example

An example file (original source) where the reset in signal comes into pads_W_0[0], a 16 bit input comes into pads_N_0[0:16], a 16 bit output comes out of pads_E_0[0:16] and a 1 bit output comes out of pads_S_0[0].

{
    "reset_in_pad": {
        "pad_bus" : "pads_W_0",
        "bits": {
            "0": { "pad_bit":"0" }
        },
        "mode": "reset",
        "width": 1
    },
    "io16in_in_arg_1_0_0": {
        "pad_bus" : "pads_N_0",
        "mode": "in",
        "width": 16
    },
    "io16_out_0_0": {
        "pad_bus" : "pads_E_0",
        "mode": "out",
        "width": 16
    },
    "io1_out_0_0": {
        "pad_bus" : "pads_S_0",
        "bits": {
            "0": { "pad_bit":"0" }
        },
        "mode": "out",
        "width": 1
    }
}