3.2.2. AIT user configuration file

AIT behaviour can be fine-tuned by overridding some configuration values using the --user_config and passing a user-provided JSON file. The values specified in the file overrides any configuration done via AIT parameters.

Current supported configuration:

• Defining placement per accelerator instance

• Defining memory interface connection per data interface

• Disabling data interfaces

• Marking data interfaces for debug

• Defining register slices pipeline stages per accelerator instance

Note

It is not mandatory to define every configuration possible for each accelerator, instance or interface in the design. If a configuration is not defined by the user configuration file, it will either take the value passed by an AIT parameter or the default one.

placement

In order to define placement for an accelerator instance, the key placement has to be placed inside the instance object of the accelerator that wants to be placed.

{
    "accs": {
        "dotproduct": {
            "instances": {
                "0": {
                    "placement": "0"
                },
                "1": {
                    "placement": "1"
                }
            }
        }
    }
}

This will constrain instance 0 of dotproduct accelerator to the SLR0 and instance 1 to the SLR1.

Accelerator instances without placement defined will be automatically managed by Vivado.

dst

The memory interface where an accelerator instance data interface will be connected can be specified with the key dst inside the interfaces object.

{
    "accs": {
        "dotproduct": {
            "instances": {
                "0": {
                    "interfaces": {
                        "v1": {
                            "dst": "2"
                        }
                    }
                },
                "1": {
                    "interfaces": {
                        "v1": {
                            "dst": "None"
                        },
                        "result": {
                            "dst": "0"
                        }
                    }
                }
            }
        }
    }
}

This will connect data interface v1 of instance 0 of dotproduct accelerator to the memory interface 2, data interface result of instance 1 to memory interface 0, while data interface v1 of instance 1 will be left dangling. Data interfaces without dst defined will be connected automatically to a memory interface following a least-occupied policy.

debug

Data interfaces can be marked for debug and connected to an ILA automatically with the key debug inside the interfaces object.

{
    "accs": {
        "dotproduct": {
            "instances": {
                "0": {
                    "interfaces": {
                        "v1": {
                            "debug": "True"
                        }
                    }
                },
                "1": {
                    "interfaces": {
                        "v1": {
                            "debug": "True"
                        },
                        "result": {
                            "dst": "False"
                        }
                    }
                }
            }
        }
    }
}

This will mark for debug data interfaces v1 of instances 0 and 1 of dotproduct and connect them to an ILA. No action will be taken for data interfaces without debug defined or defined as False.

regslice_pipeline_stages

The number of pipeline stages created for each section of an SLR-crossing register slice can be configured with the key regslice_pipeline_stages for each accelerator instance.

{
    "accs": {
        "dotproduct": {
            "instances": {
                "0": {
                    "regslice_pipeline_stages": "2:3:4"
                },
                "1": {
                    "regslice_pipeline_stages": ":auto:1"
                }
            }
        }
    }
}

This will configure the register slices affecting instance 0 of dotproduct as having 2 pipeline stages in the source section, 3 in the middle and 4 in the destination one. Register slices of instance 1 of the dotproduct accelerator the following way: default (or the value passed to AIT by the --regslice_pipeline_stages parameter) for the source section, auto for the middle one (meaning that Vivado will automatically decide the number of stages) and 1 for the destination section.