On 03/16/2012 06:37 PM, Tom Rondeau wrote:
On Fri, Mar 16, 2012 at 8:41 AM, Zhonghua <zhong...@sics.se
<mailto:zhong...@sics.se>> wrote:
Hi all,
After a period of using gnu radio, I have a problem of how to
understand the stream. I got an information from a literature
says: 'From the high level point-of-view, infinite streams of data
flow through the ports. At the C++ level,streams are dealt with in
convenient sized pieces, represented as contiguous arrays of the
underlying type.' In almost each signal processing block we can
see the definition of 'general_work' has this format:
general_work(int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
Some literatures say the 'noutput_items' variable represents the
items number of one piece of the stream. So the first question is
what on earth the size of this variable? where dose it be
specified? For example if A block connects to B block, how can
ensure the 'noutput_items' of A block equal to the 'ninput_items'
(presume B block only has one input stream).
In an concrete instance, in gr_squelch_base_cc.cc, we can see the
last program as:
if (d_state != ST_MUTED)
out[j++] = in[i]*gr_complex(d_envelope, 0.0);
else
if (!d_gate)
out[j++] = 0.0;
If we set d_gate as False(Actually in case of high sample rate it
has to be set as False), when the input power is lower than the
threshold(means the d_state should be as ST_MUTED), the out[j]
shall get nothing. That means at this point there is no output
data. So how the sequential block recognise this point? For
instance the sequential block is ieee802_15_4_demod, how could it
know where is this lost point? If only one point lost from the
squelch block, is that means the whole piece of stream and even
the whole package could not be demodulated correctly?
We can set the instance in more precise condition. If there are
two pieces of stream: stream A and stream B. Assume each
noutput_items is 10, that is to say we have A[0], A[1] ....to A[9]
and B[0] to B[9]. If A[0] has lost, then the stream entering into
the sequential demodulation block is A[0](lost),A[1]....A[9]? Or
is A[1],A[2]....B[0]?
If A[0] is valid, A[1] has lost, dose that mean the first piece of
stream would not be demodulated correctly? If one package need
both these two pieces of stream, dose it mean this package would
not be demodulated correctly?
Any answer is greatly appreciated.
Sincerely,
Zhonghua
Zhonghua,
This is a really complicated question to answer without giving you a
full essay. All of this happens in the scheduler, so if you want to
know more, study the code for the thread-per-block scheduler in
gnuradio-core/src/lib/runtime. It's the gr_block_executor that looks
at the read/write pointers to each blocks buffer and determines how
many samples are available to be read and how many samples a block can
write.
Tom
Hi Tom,
Thank you for your information. I think you have answered the first
question that where and how dose the size be determined. To the detailed
question, do you think if one item lost, all this package will lose? And
in my last instance, do you think which assemblage will be sent to the
sequential block? Thank you again!
Zhonghua
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