# Build C++ processing block that adds a preamble **URL:** \ **Category:** GNU Radio\ **Created:** [July 20, 2015, 11:00am UTC](https://www.ruby-forum.com/t/build-c-processing-block-that-adds-a-preamble/242714 "2015-07-20T11:00:45Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![gabri187](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/e9bcb4/32.png) [@gabri187](https://www.ruby-forum.com/u/gabri187)\ **Post date:** [July 20, 2015, 11:00am UTC](https://www.ruby-forum.com/t/build-c-processing-block-that-adds-a-preamble/242714/1 "2015-07-20T11:00:45Z")
Hello, I am trying to build my own block. The block should operate as follows: - The block receive the sequence of the input stream. - The block divides the input sequence in blocks of d\_pkt\_len elements, a predefined value of packet length (unsigned int d\_pkt\_len), and attach to the beginning of the sequence a word of specified length of samples (unsigned int d\_sync\_word\_len). - In this example the word is set to be just 0’s for simplicity. d\_pkt\_len and d\_sync\_word\_len are meant to be input parameters in the final block. For instance, if input is (1,1,1,1,1,1) and d\_pkt\_len=6, d\_sync\_word\_len=4, the output should be (0,0,0,0,1,1,1,1,1,1). If input is (1,1,1,1,1,1) and d\_pkt\_len=3, d\_sync\_word\_len=4, the output should be (0,0,0,0,1,1,1,0,0,0,0,1,1,1). This was a bit confusing for me when it came to code forecast function, since, the output number of items really depends on the input and the parameter d\_pkt\_len. I used set\_output\_multiple(). The issue is, I built the block, and one of the tests failed. Giving me the following error: > > build$ ctest -V -R > > UpdateCTestConfiguration from > > :/home/comlab/Desktop/Gabri/mimo/gr-sync/build/DartConfiguration.tcl > > UpdateCTestConfiguration from > > :/home/comlab/Desktop/Gabri/mimo/gr-sync/build/DartConfiguration.tcl > > Test project /home/comlab/Desktop/Gabri/mimo/gr-sync/build > > Constructing a list of tests > > Done constructing a list of tests > > Checking test dependency graph… > > Checking test dependency graph end > > test 1 > > Start 1: test\_sync 1: Test command: /bin/sh “/home/comlab/Desktop/Gabri/mimo/gr-sync/build/lib/test\_sync\_test.sh” 1: Test timeout computed to be: 9.99988e+06 1: 1: 1/2 Test #1: test\_sync … Passed 0.00 sec test 2 Start 2: qa\_sync\_ff # 2: Test command: /bin/sh “/home/comlab/Desktop/Gabri/mimo/gr-sync/build/python/qa\_sync\_ff\_test.sh” 2: Test timeout computed to be: 9.99988e+06 2: thread[thread-per-block[1]: \]: pmt\_dict\_keys: wrong\_type : # 2: thread[thread-per-block[1]: \]: pmt\_dict\_keys: wrong\_type : # 2: F 2: ## 2: FAIL: test\_001\_t ( **main**.qa\_sync\_ff) 2: ## 2: Traceback (most recent call last): 2: File “/home/comlab/Desktop/Gabri/mimo/gr-sync/python/qa\_sync\_ff.py”, line 47, in test\_001\_t 2: self.assertFloatTuplesAlmostEqual(expected\_result, result\_data, 6) 2: File “/usr/local/lib/python2.7/dist-packages/gnuradio/gr\_unittest.py”, line 88, in assertFloatTuplesAlmostEqual 2: self.assertEqual (len(a), len(b)) 2: AssertionError: 10 != 0 2: 2: 2: Ran 1 test in 0.264s 2: 2: FAILED (failures=1) 2/2 Test #2: qa\_sync\_ff …\*\*\*Failed 0.43 sec 50% tests passed, 1 tests failed out of 2 Total Test time (real) = 0.43 sec The following tests FAILED: 2 - qa\_sync\_ff (Failed) Errors while running CTest I was trying to get some info from this, but I wasn’t able so far. In addition I tried to make the xml file just to try it in GNURadio-Companion but It gave me error, I guess it has to be with the test error. If anyone is able to help me or give me some tip to fix that it would be very nice. I have spent so much time in this simple block. I attach the sync\_ff\_impl.cc, sync\_ff\_impl.c and qa\_sync\_ff.py files. Thanks in advance.