Thanks for the thoughts Sean. I hadn't thought of calling early to give
the tuner time to settle. I'll also have a look at the burst tagger
example as you suggested. I think I should be able to make a block with
only an input and put it in parallel with the other blocks in my
circuit. This should save some processing power in not needing to copy
the samples to the output. I guess what I was really asking was whether
it had to accept samples at all? As in, could a block be made with no
input or output and would its work function be called at a set interval
of time (or even at all)? Probably not a request made often and I don't
think it would take much extra processing power to just feed it the
samples. Still, I thought it was worth looking into.
-Dan
On 6/29/2012 7:31 PM, Nowlan, Sean wrote:
You can put a block in sequence with the samples that does two things
in the work() function:
1)copy the input buffer to the output buffer using memcpy or something
similar since it doesn't look like you need to process the samples at all
2)keep track of "number of samples remaining before re-tune" in a
local variable that you set to NSAMPS_PER_TUNE, and decrement it by
noutput items as you described. If this variable gets down to 1 (or
0?) re-set it to NSAMPS_PER_TUNE and call the set_command_time()
function to retune. You'll have to follow the lead of the burst
tagging example to know precisely what absolute time you need to
retune, and you also have to make sure the re-tune command gets called
with some lead-time, so I'm not quite sure how to handle this.
This is just a rough guess of how to do it; I'm sure there are other
nuances. With this approach you shouldn't need to worry about how many
samples were passed to your work() function since you always decrement
your count variable by how many you received.
Hope that helps!
Sean
*From:*discuss-gnuradio-bounces+sean.nowlan=gtri.gatech....@gnu.org
[mailto:discuss-gnuradio-bounces+sean.nowlan=gtri.gatech....@gnu.org]
*On Behalf Of *Daniel Labarowski
*Sent:* Friday, June 29, 2012 4:21 PM
*To:* discuss-gnuradio@gnu.org
*Subject:* [BULK] [Discuss-gnuradio] How many samples per call to work
function?
*Importance:* Low
Hello,
I am going to be making a C++ block which will either change the value
of a variable (which would be passed to it by a pointer) or call the
tune function of a USRP sink (passed by a pointer) after a certain
number of samples have been passed to the block. This is related to my
question here.
<http://old.nabble.com/Tunning-USRP-From-Seperate-C%2B%2B-Block--td33970855.html#a33970855>In
order to do this, I need to establish how often the work function is
called. From my past experience writing GNURadio signal processing
blocks, it looks like around 8190 samples are passed to the blocks
work function each time it is called, but this tends to vary wildly.
Also, I haven't tested whether this is dependent on data format of the
input/output. My current plan to build the block is to increment a
(local, not the on being passed) variable by noutput items each time
the work function is called. Once a certain number of samples have
been handled by the block, I will change the frequency. I was
wondering if it is even possible to construct a block with no output
or input, and if it is possible whether the work function would ever
get called and whether its noutputitems (or ninputitems) would
correspond to the number of samples flowing through the rest of the
flowgraph? If it cant be done this way, I suppose it would be no real
issue to give the block an input so that it can count ninputitems then
just not do anything with the input items. Just trying to get a feel
for the best way to do this and to find out, in general, how
frequently the work function of the block is called and how many
samples are passed with each call? Thanks!
-Dan
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