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Re: [Discuss-gnuradio] ramping down (tx_empy continued)

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] ramping down (tx_empy continued)
Date: Tue, 16 Jan 2007 08:22:58 -0800
User-agent: Mutt/1.5.9i

On Tue, Jan 16, 2007 at 07:41:58AM -0800, Brett Trotter wrote:
> I've been pondering a few ways to do the wait and ramp down (wait something
> like 16 clocks and then ramp down by right shifting on each clock)- but to
> do so, I need to know what the last value was so I can shift it. Will
> tx_i_*/tx_q_* remain persistent between clocks (my deduction was yes?) If
> so, my plan here was to have a reg that holds a 4-bit counter that starts at
> 15 whenever tx empty goes high/true and then just keep right shifting the
> appropriate value (based on load_next) until zero (or just keep shifting
> until data since 0 >> 1 = 0- would that save on logic?).

Brett, if you jam zero's into the front of the signal processing path
like you suggested in your first message, you don't have to ramp the
input down.  The interpolating filters will take care of the
discontinuity for you.

No need to make this hard.  I think your original code will work.

> Then I had one question- is there ever a situation where we're out of data
> for any number of channels, but there's still one transmitting (e.g. can
> tx_empty ever be asserted when we're feeding just one of the 4
> destinations?). I'm under the (mistaken?) impression that tx_empty asserts
> when we stop feeding the buffer altogether (underrun)- so without doing some
> digging- do we fill zero's to the channels we're not using when we're still
> feeding one of them?
> With those answered, I think I can probably try and get a version done today
> for testing.


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