Problems when passing messages to a source

[mikotaFull]

Good morning @jacobagilbert ,

I am writing to you because you solved the problem of someone in the issue https://github.com/gnuradio/gnuradio/issues/4239, and I am facing a pretty similar problem.

I want to generate a source controlled by voltage. Basically, I send messages to a source in order to change its amplitude.
I have built a block to generate messages and pass them to the source. To do so, I created an "embedded python block " and used part of the code of the " qa_python_message_passing.py " which is in the gnuradio's repository.

When I execute the graph in gnuradio I get the error : "File "/home/epy_block_0.py", line 29, in work self.msg_list.append(pmt.from_double(input_items[0][:]))
File "/usr/lib/python3/dist-packages/pmt/pmt_swig.py", line 1985, in from_double return _pmt_swig.from_double(x)
TypeError: in method 'from_double', argument 1 of type 'double'
thread[thread-per-block[4]: <block message generator(2)>]: SWIG director method error. Error detected when calling 'feval_ll.eval'"

I don't really understand what is wrong, why the pmt.from_double method doesn't work if the argument I'm passing is a double?
Please could you give me some guidance ? I am new to gnuradio and python, any help will be appreciated...
I attach the python code of the block (the message generator) and the GRC flowgraph.
thank you in advance.

[jacobagilbert]

Hello @mikotaFull

The issue here appears to be that input_items[0][:] is not a double, it is a list of floating point values.

There are other issues here (you probably do not want to be publishing a message for every single item you receive in, and you are growing self.msg_list indefinitely... but if you index the specific item in the input list you want to use it will 'work'.

To step through various input values try this (untested, caveat emptor):

def work(self, input_items, output_items):
  self.msg_port_pub(pmt.intern('out_port'), pmt.cons(pmt.intern('ampl'), pmt.from_double(input_items[0][0]))
  time.sleep(1)
  return 1

This is not a generally useful block, but should let you see how the mechanics of what you are trying to do works. Each call it will use the first input sample to set the amplitude, then sleep for 1 second before consuming one sample. The next work call will consume the second sample, then the third, etc.

[mikotaFull]

Hello @jacobagilbert

Thank you for your reply and sorry for the delay in mine.
Despite the changes my block still doesn't work and I wanted to find the problem by myself, but until now I can't.

when I use:

    def work(self, input_items, output_items):
       self.msg_port_pub(pmt.intern('out_port'), pmt.cons(pmt.intern("ampl"), pmt.from_double(input_items[0][0]))) 
       time.sleep(1)
       return 1

I have the error : self.msg_port_pub(pmt.intern('out_port'), pmt.cons(pmt.intern("ampl"), pmt.from_double(input_items[0][0])))
AttributeError: 'message_generator' object has no attribute 'msg_port_pub' .
And I can't understand why if in the initial code (below) the function message_port_pub is called as I do in mine.

    def work(self, input_items, output_items):
        inLen = len(input_items[0])
        while self.msg_ctr < len(self.msg_list) and \
                (self.msg_ctr * self.msg_interval) < \
                (self.nitems_read(0) + inLen):
            self.message_port_pub(pmt.intern('out_port'),
                                  self.msg_list[self.msg_ctr])
            self.msg_ctr += 1
        return inLen

But for example when I use the code below I have no error BUT the amplitude of the source doesn't change

    def work(self, input_items, output_items):
       self.message_port_pub(pmt.intern('out_port'), pmt.cons(pmt.intern("ampl"), pmt.from_double(3.0)))
       return 1

Please can you explain to me what I'm doing wrong this time?
Thank you.