Hi 奕佑,
this question reveals that you have not considered GNU Radio to not
be bound by real time.
As samples are "bare numbers", they don't have a time. Thus, GNU
Radio nor any of the blocks involved care about how much time has
passed in the real world. Thus, for your block, while no message
occurs time "does not pass". And you can only generate samples in
the work function.
Therefore, yes, it can be done, but you'll have to calculate in your
work how many samples you wanted to produce in the time since the
last call to work.
If you have a hardware sink or source involved though, this is
*never* the correct approach, since you will end up with two
competing clocks, and that will, over a longer time, lead to over-
or underflows. You can solve this issue by either using a hardware
sink that accepts bursts of data, so you don't have to zero pad, or
by having a block that passes through input samples (e.g. from a
constant 0 source) and adds message-generated samples when they
occur.
Greetings,
Marcus
On 07.08.2014 14:53, 奕佑 wrote:
Hello Martin,
If you create a block which input is message and output is float. And
message is arrive discrete just like packet in network, I want the block
output port will output 0 when no message arrive at input port. Can I do
that?
Why I ask this question is that I a while ago I trying to create a
communication system which I defined and there has two kinds of channel one
is control channel and the other one is message channel like the GSM system
I think so, and I'm using FDD. And control channel is using gmsk modulation
and message channel is using fm modulation because I just want to transmit
audio, I using enough BW to avoid aliasing. After gmsk mod and fm mod, I
add them together but result failed, because add block in gnuradio will
wait when two input data and add one-by-one so if if port one data is much
more then port two, and the add will hold port one data and wait port two
data then add one-by-one.
I have recreate the same situation and past in the mail, it is python file
and can test it to check the problem
Here is my setting : I have two source one is audio source and the other is
packet, and I add it together and output to audio sink. Important audio
source will generate data when program start. The first 5 second no packet
is send. After 5 second packet source will send 1000 packets, meantime,
speaker have sound, and if you have say something in first 5 seconds, you
will hear what you say in the first 5 second now.
---------------------------------------------------------
#!/usr/bin/env python
##################################################
# Gnuradio Python Flow Graph
# Title: Top Block
# Generated: Thu Aug 7 20:16:29 2014
##################################################
from gnuradio import eng_notation
from gnuradio import gr
from gnuradio.eng_option import eng_option
from gnuradio.filter import firdes
from optparse import OptionParser
from gnuradio import digital
from gnuradio import audio
from gnuradio import blocks
from time import sleep
class top_block(gr.top_block):
def __init__(self):
gr.top_block.__init__(self, "Top Block1")
##################################################
# Variables
##################################################
self.samp_rate = samp_rate = 32000
##################################################
# Blocks
##################################################
self.digital_gmsk_mod_0 = digital.gmsk_mod( samples_per_symbol=2,
bt=0.35, verbose=False, log=False, )
self.digital_mod_pkts_0 = digital.mod_pkts(self.digital_gmsk_mod_0,
access_code=None, msgq_limit=4, pad_for_usrp=False)
self.audio_source_0 = audio.source(samp_rate, "", True)
self.audio_sink_0 = audio.sink(samp_rate, "", True)
self.blocks_add_xx_0 = blocks.add_vcc(1)
self.blocks_float_to_complex_0 = blocks.float_to_complex(1)
self.blocks_complex_to_real_0 = blocks.complex_to_real(1)
self.blocks_multiply_const_vxx_0 = blocks.multiply_const_vcc((0.01,
))
##################################################
# Connections
##################################################
self.connect((self.blocks_add_xx_0, 0),
(self.blocks_complex_to_real_0, 0))
self.connect((self.blocks_complex_to_real_0, 0),
(self.audio_sink_0, 0))
self.connect((self.audio_source_0, 0),
(self.blocks_float_to_complex_0, 0))
self.connect((self.audio_source_0, 0),
(self.blocks_float_to_complex_0, 1))
self.connect((self.blocks_float_to_complex_0, 0),
(self.blocks_add_xx_0, 0))
self.connect((self.digital_mod_pkts_0, 0),
(self.blocks_multiply_const_vxx_0, 0), (self.blocks_add_xx_0, 1))
def send_pkt(self, payload='', eof=False):
self.digital_mod_pkts_0.send_pkt(payload, eof)
if __name__ == '__main__':
parser = OptionParser(option_class=eng_option, usage="%prog: [options]")
(options, args) = parser.parse_args()
tb = top_block()
tb.start()
sleep(5)
for i in range(0, 1000):
tb.send_pkt('a')
raw_input('Press Enter to quit: ')
tb.stop()
tb.wait()
------------------------------------------
Jeff Guo
2014-08-07 19:07 GMT+08:00 Martin Braun <address@hidden>:
On 08/07/2014 12:54 PM, 奕佑 wrote:
Hello,
Is there any way to combine continuous block (like audio source) and
discrete block (like message source) ? Question 1
Combine how? You can do that in your own blocks, sure. Maybe stream tags
are what you want?
I using add block to add them together, but it failed. It work well when
the discrete block output data like continuous block but discrete block
means there is not output data continuous, it output data when something
trigger.
Can I write a block which input is message and output is like float, and
output will always generate like 32k samples but input doesn't have 32k
samples suppose this block is sync. Is there any solution ? Question 2
You can write a block who's input is message and output is float. I
didn't really understand the rest of the question.
M
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