Re: [Discuss-gnuradio] Delay block controlled by input

[Marcus Müller]

Hi,

On 08.10.2014 14:38, Carlos Alberto Ruiz Naranjo wrote:
> Delay Block is controlled by Satellite Orbit and Satellite Orbit by
> "simulated clock". The output of Satellite Orbit is the delay (samples).
> Can I know the nitems_read of Delay Block from other block (Satellite
> Orbit)?
Yes. It's a public function, as you can see in the documentation I linked.
>
> Maybe a solution is to introduce Orbit Satellite in Delay block, but this
> is really inefficient to do tests.
Good point, but you should be able to test your "calculate transmission
delay from an integer" functionality externally; also, there's no reason
to have something like a class "delay_calculator", with methods you call
from your modified delay block. You can test that very easily isolated.
>  And a problem if I want to change the
> Delay block for your solution (FFT).
Well, yes, if you change approaches, the old approach will no longer
apply. That's a design decision you'll have to make.

>
> Really the delay is in the non-modulated signal.
I don't understand this sentence, sorry.

Greetings,
Marcus

>
>
>
> 2014-10-08 13:43 GMT+02:00 Jeff Long <address@hidden>:
>
>> If you're comparing real time (system clock) to your sample stream, you'll
>> get jitter, not drift, using a throttle. Throttle maintains a sample rate
>> over time, but operates on blocks, and also is running under a non-realtime
>> operating system.
>>
>> If you're talking about drift between the clock on your receiver and the
>> real world, that's normal and you have to find ways to deal with it.
>>
>> - Jeff
>>
>> On 10/08/2014 07:33 AM, Carlos Alberto Ruiz Naranjo wrote:
>>
>>> Yes, it is not a real time clock. This "clock" tracks the current time
>>> of the signal in GNURadio.clock2 and clock1 have a drift because the
>>> number of counted samples are different.
>>>
>>> For example, if it pass 10230000 samples the delay block is entering the
>>> delay in signal time = 1 second.
>>> 1 second in the real world (later I replay the signal with a USRP).
>>>
>>> 2014-10-08 13:18 GMT+02:00 Martin Braun <address@hidden
>>> <mailto:address@hidden>>:
>>>
>>>     If you don't have hardware involved, you have no 'clock'. And as such,
>>>     it can't drift.
>>>
>>>     M
>>>
>>>     On 10/08/2014 12:29 PM, Carlos Alberto Ruiz Naranjo wrote:
>>>     > Sorry, I have explained bad: S
>>>     > I have the signal saved in a file and 10230000 samples are one
>>> second
>>>     > (in the real world).
>>>     >
>>>     > In the first graph I have two clocks (counters samples). When
>>> passing
>>>     > 102300 samples it increase0.01 seconds.
>>>      > In the first watchthis time controls the position of the
>>>     satellite and
>>>      > hisdelay in this time. It allows to know what signal time is
>>>     passing in
>>>     > the delay block.
>>>     >
>>>     >
>>>     > But I have a problem: clock 2 (a test clock) and clock 1 haven't the
>>>     > same time; it has a drift.
>>>     >
>>>     >
>>>     > Then, I must use clock 2 (
>>>     > count the samples in the delay block output, not input). But it
>>> creates
>>>     > a loop.
>>>     >
>>>     >
>>>     >
>>>     > 2014-10-08 12:07 GMT+02:00 Marcus Müller <address@hidden
>>> <mailto:address@hidden>
>>>      > <mailto:address@hidden <mailto:address@hidden
>>>>>> :
>>>     >
>>>     >     Hello Carlos,
>>>     >     On 08.10.2014 09:10, Carlos Alberto Ruiz Naranjo wrote:
>>>     >     > I generate the signal from a file (10230000 samples/s) to a
>>> file. My
>>>     >     > sampling clock drifts significantly :S
>>>     >     No. Unless I misunderstood you, you have a big misconception:
>>>     >     "sampling clock" is *not* the rate at which your samples pass
>>> through
>>>     >     your processing chain (ie. GNU Radio). It is the time base at
>>> which they
>>>     >     are measured, or simulated to, mathematically.
>>>     >     The device/software that actually captures the samples and
>>> saves them
>>>     >     has a fixed clock. If that clock changes too much a) compensate
>>> that in
>>>     >     software, if possible or b) get a better device.
>>>     >     This is digital signal processing. Real world time has *no*
>>> meaning
>>>     >     here, everything is measured relative to the interval between
>>> two
>>>     >     sampling times. You can process the signal as fast or slow as
>>> you want
>>>     >     to (as long as that doesn't lead to things like overflows), and
>>> nothing
>>>     >     in the processing chain should care.
>>>     >     >
>>>     >     > - Picture one: Counter Clock 2 is correct but Counter Clock 1
>>> no.
>>>     >     > Then I should use the second configuration, but it is not
>>> allowed because I
>>>     >     > have a loop, right?
>>>     >     I don't understand your graph, sorry :(
>>>     >
>>>     >     Greetings,
>>>     >     Marcus
>>>     >
>>>     >
>>>     >
>>>     >
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