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1.4. Configuration

The BusMatrix is designed to allow for all configurations of input and output ports, up to a maximum of eight:

  • from two to eight input ports

  • from one to eight output ports

  • round-robin or fixed arbitration.

This gives a total of 112 different configurations (7 × 8 × 2). A script called is supplied to allow the construction of any version that is required.

The script is located in both the vhdl and vlog directories. To obtain information on the usage of the script, run the script with the help switch:

  > --help

This prints the following information:

Purpose:  Builds particular configurations of the BusMatrix
   Builds a BusMatrix component with a given number of input
   ports <inports>, a given number of output ports <outports>
   and a particular arbitration scheme.
   --inports=NUM           Number of input ports (2,3..8)
   --outports=NUM          Number of output ports (1,2..8)
   --arb=SCHEME            Arbitration scheme (f - fixed,
                           r - round-robin)
   --all                   Builds all possible configurations
   --verbose               Prints progress information
   --help                  Prints this help

To run the script and build all possible variants use the following command:

  > --all --verbose

When run, the script generates the RTL for the required BusMatrix in the built directory. The name of the directory has the maximum number of the input and outputs as found in the RTL and this is one less than might be expected, because the ports are numbered from zero up to the maximum number. For example, a BusMatrix with three input ports and five output ports is found in the directory named input2_by_output4_fixed.

If only a single configuration of the BusMatrix is required, the script can be run to only build that option. Three parameters are required:

  • number of input ports

  • number of output ports

  • arbitration scheme, which can be either fixed priority or round-robin

To build a BusMatrix with three input ports, five output ports, and a fixed priority arbitration scheme, use the following command:

  > --inports=3 --outports=5 --arb==fixed

Source code pragmas

The different configurations are generated from a source design that is constructed for the maximum configuration of eight input ports and eight output ports. Throughout this design pragmas are used to indicate the portions of code that can be removed for smaller BusMatrix configurations.

For example, the code required for just one output port (port number 0) is followed by the pragma

-- busswitch output0

the code required for two output ports (up to port number 1) is followed by the pragma

-- busswitch output1

and so on, until finally the code required for all output ports (up to port number 7) is followed by the pragma

-- busswitch output7

Therefore, to generate the code required for a two output port configuration the script is used to remove all the RTL code between the -- busswitch output1 and -- busswitch output7 pragmas.

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