Interconnect generation¶

Interconnects enable the connection of multiple interfaces in a many-to-many topology, as opposed to the traditional one-to-one manager-subordinate connection. This approach facilitates data transmission between multiple IP cores over a single interface, with the interconnect serving as an middle-man.

Each manager can communicate with any subordinate connected to the interconnect. Every connected subordinate must be assigned a predefined address range, allowing the interconnect to route data based on the address specified by the manager.

A typical interconnect topology diagram is shown below.

In order to generate an interconnect, you have to describe its configuration in the Design description under the interconnects key in the following format, as specified below:

Format¶

The interconnects key must be a direct descendant of the design key in the Design description.

interconnects:
  {interconnect1_name}:
    # Specify clock and reset to drive the interconnect with
    clock: [{ip_name, clk_port_name}]
    reset: [{ip_name, rst_port_name}]
    # Alternatively you can specify a connection to an external port of this design:
    # clock: ext_clk_port_name
    # reset: ext_rst_port_name

    # Specify the interconnect type.
    # See the "Supported interconnect types" section below for available types
    # and their characteristics
    type: {interconnect_type}

    # custom parameter values for the specific interconnect type
    parameters:
      {parameters_name1}: parameters_value1
      ...

    # specify managers and their interfaces connected to the bus
    managers:
      {manager1_name}:
        - {manager1_interface1_name}
        ...
      ...

    # specify subordinates, their interfaces connected to the bus and their bus parameters
    subordinates:
      {subordinate1_name}:
        {subordinate1_interface1_name}:
          # requests in address range [address, address+size) will be routed to this interface
          address: {start_address}
          size: {range_size}
        ...
      ...
  ...

Supported interconnect types¶

Wishbone Round-Robin¶

This interconnect only supports Wishbone interfaces for managers and subordinates. It supports multiple managers, but only one of them can drive the bus at a time (i.e. only one transaction can be happening on the bus at any given moment). A round-robin arbiter decides which manager can currently drive the bus.

Parameters¶

Subordinate¶

• addr_width - bit width of the address line (addresses access data_width-sized chunks)

• data_width - bit width of the data line

• granularity - access granularity - the smallest unit of data transfer that the interconnect can transfer. Must be: 8, 16, 32, 64

• features - optional, list of optional wishbone signals, can contain: err, rty, stall, lock, cti, bte

Known limitations¶

The currently known limitations are:

• only word-sized addressing is supported (in other words - consecutive addresses can only access word-sized chunks of data)

• crossing clock domains, down-converting (initiating multiple transactions on a narrow bus per one transaction on a wider bus) and up-converting are not supported

AXI¶

This interconnect only supports AXI4 interfaces for managers and subordinates. Uses pulp-platform/axi as dependency.

Parameters¶

• atop - True or False, enables or disables atomic operations

Manager¶

• id_width - bit width of ID signals