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Altera_Forum's avatar
Altera_Forum
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17 years ago

fan out problem in assigning

I want to implement a CAM/RAM combination.

the altera megawizard function dosn't provide a seperated bus CAM for (read_data & write_data)

I have to send incoming_label to both: CAM and CPU but I facing with fan_out problem in assignment.

providing input/output registering for CAM dosn't work

how can i fix this problem?

currently i don't want to design a new CAM device with separated bus.

thanks.

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3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    You may design a bus multiplexer block which reads simultaneously the label_out and the output of the CPU and enables the output automatically when one of the two inputs has to be passed to the CAM-RAM block. In this way the two input busses will not feed the input simultaneously, thus avoiding the problem.

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    yes thanks, I solved it after posting this thread with bus_mux in megafuncions it was very easy and exactly as you said, but I afraid about time conflicts with an interval between two components I though that using a MUX between two components limits my f_max more....but now I think just two main approach remains:

    redesigning the CAM with separated bus for writing and reading or using a MUX.

    the first approach will take long time to design if I want to implement comparable CAM with ALT_CAM megafunction in a synthesis perspective.

    so I have to sacrifice the f_max for this.

    actually if I don't mistake on these thoughts, but sincerely thanks for your comment that's exactly a right solution.

    Best Regards
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    You are right, you will certainly see a decrease in the fmax, but typically the overall performance will be mostly dependent on the memory access time so you won't see a high decrease only for the presence of the bus multiplexer.