I see, thanks~~ 2009/12/22 Eric Blossom <[email protected]>
> On Tue, Dec 22, 2009 at 12:22:29PM +0800, zhi yan wrote: > > Hi All, > > > > I am confused of the Set_history() which is a function of gr_block, what > is > > the function of this function? thanks~~ > > > > It exists so that you can implement an "inline delay line", or similar > functionality. The primary user of set_history are the FIR filters, > but there is other code that uses it. The default value of history is > 1, which is admittedly confusing, but is how it was historically > defined. > > To give a concrete example, if you subclass gr_sync_block (which is > 1:1 from input to output) and don't call set_history in the > constructor, when your work function is called with a value of > noutput_items = N, there are guarenteed to be N valid samples in the > input vector, indexed from 0 to N-1. > > If in the constructor you call set_history(2), when work is called > with a value of noputout_items = N, there are guarenteed to be N + 1 > valid samples in the input vector, indexed from 0 to N. > > If in the constructor you call set_history(H), when work is called > with a value of noputout_items = N, there are guarenteed to be > N + H - 1 valid samples in the input vector, indexed from 0 to N + H - 2. > > The other subclasses of gr_block work similarly. Take a look at their > forecast routines for the details. > > On the first call to work, the first H - 1 samples will be zero. > > Eric >
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