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 Driving not connected bus bits 

Last post Thu, Dec 21 2006 7:14 AM by archive. 1 replies.
Started by archive 21 Dec 2006 07:14 AM. Topic has 1 replies and 1166 views
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  • Thu, Dec 21 2006 7:14 AM

    • archive
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    Driving not connected bus bits Reply

    Hello to all RC users,
    I have some hierarchical ports of subdesigns, which are currently unused.
    The are not driven inside the subdesign and not connected at the higher level.
    RC decided to drive them with 1'b0 - assign output_pin[0] 1'b0
    There is an attribute, that is responsible for such behaviour:
    rc:/> get_attr hdl_undriven_signal_value /
    none

    The options are 1, 0, Z, none.
    It seems that RC ignores this attribute.

    Any suggestion, how to eliminate driving of the unconnected bit would be appresiated.

    Regards,


    Originally posted in cdnusers.org by Stalker
    • Post Points: 0
  • Thu, Jan 18 2007 12:44 PM

    • archive
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    RE: Driving not connected bus bits Reply

    There are 2 attributes that control the connectivity of undriven logic. The first that you mentioned is hdl_undriven_signal_value. This attribute controls the drive value of the undriven signals in a module.

    attribute name: hdl_undriven_signal_value
    category: elab (controls elaboration)
    object type: root
    access type: read-write
    data type: string
    default value: none
    help: Connects each undriven signal in a module to the specified value unless the none value is specified.
    more help: permitted values: { 0 1 x X z Z none }


    Another attribute, hdl_undriven_output_port_value, controls how undriven output ports will be handled.


    attribute name: hdl_undriven_output_port_value
    category: elab (controls elaboration)
    object type: root
    access type: read-write
    data type: string
    default value: none
    help: Connects each undriven output port in a module to the specified value unless the none value is specified.
    more help: permitted values: { 0 1 x X z Z none }


    Both of these attributes should be set before elaboration to achieve the desired effect.

    There is another user utility that is available if you want to delete unused ports and subports.This command is called delete_unloaded_undriven and is only available after adding the following command to your script : "include load_etc.tcl"

    rc:/> delete_unloaded_undriven -h

    Usage: delete_unloaded_undriven [-disconnect] [-all] [-force_bit_blast] [] [> file]

    [-disconnect]:
    disconnects the constant connected subports/ports
    [-all]:
    deletes/disconnects in the top level also
    [-force_bit_blast]:
    removes indiviual bits of a bus by bitblasting the module
    []:
    specify design name


    This command and the attributes listed above should allow you to achieve the desired connectivity in your design.


    Originally posted in cdnusers.org by sthomson
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Started by archive at 21 Dec 2006 07:14 AM. Topic has 1 replies.