# GRC Hier block with vector IO not working as expected

**URL:** <https://www.ruby-forum.com/t/grc-hier-block-with-vector-io-not-working-as-expected/238406>\
**Category:** GNU Radio\
**Created:** [January 8, 2014, 10:00pm UTC](https://www.ruby-forum.com/t/grc-hier-block-with-vector-io-not-working-as-expected/238406 "2014-01-08T22:00:57Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [January 8, 2014, 10:00pm UTC](https://www.ruby-forum.com/t/grc-hier-block-with-vector-io-not-working-as-expected/238406/1 "2014-01-08T22:00:57Z")

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Hi list,

I’m currently in the process of porting my gr-drm project to the 3.7 API  
and now I’m a little bit stuck and hope that someone here can help me.

I want to create a hier block (in GRC) that accepts vectors as input and  
output. Their size is controlled by parameters like vlen\_in and  
vlen\_out.  
Unfortunately, the IO size of the generated hier block always stays 1,  
no  
matter what I use as parameter. I attached a minimal (pure GNU Radio)  
example flow graph and hier block that reproduces my problem. Maybe I  
overlooked something obvious, but I don’t get why this is not working.

If someone had the time to try this and could report if it works (it  
does  
not for me), I would be very grateful.

I’m on Ubuntu 12.10 and have GNU Radio v3.7.2.1-116-ge751e54a installed.

Regards,  
Felix W.

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**Author:** ![Felix\_W](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/bb73d2/32.png) [@Felix\_W](https://www.ruby-forum.com/u/Felix_W)\
**Post date:** [January 8, 2014, 10:59pm UTC](https://www.ruby-forum.com/t/grc-hier-block-with-vector-io-not-working-as-expected/238406/2 "2014-01-08T22:59:59Z")

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Hi Felix,

I can reproduce it. Problem is that the generated ‘xml’ file is not  
generated correctly. The parameter ‘vlen’ should be written as ‘$vlen’  
in  
the xml files source/sink section but it is written as ‘vlen’. Thus  
‘vlen’  
is treated as the value. Happens with ‘v3.7.2-11-g3b27cc47’. I don’t  
know  
how to fix it though.

Happy hacking  
Johannes