# C++ block that generate extra data **URL:** \ **Category:** GNU Radio\ **Created:** [September 29, 2011, 4:15pm UTC](https://www.ruby-forum.com/t/c-block-that-generate-extra-data/212318 "2011-09-29T16:15:07Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\ **Post date:** [September 29, 2011, 4:15pm UTC](https://www.ruby-forum.com/t/c-block-that-generate-extra-data/212318/1 "2011-09-29T16:15:07Z")
Hello, i have a block that takes 3 bytes of data in and output 4bytes of data (3:4). It’s possible to generate, sometimes, extra output? I mean, sometimes it take 3 bytes and output 5 bytes. It’s possible? How i tell to the scheduler? Thank you ---
**Author:** ![Mattia\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@Mattia\_R](https://www.ruby-forum.com/u/Mattia_R)\ **Post date:** [September 29, 2011, 4:21pm UTC](https://www.ruby-forum.com/t/c-block-that-generate-extra-data/212318/2 "2011-09-29T16:21:56Z")
On Thu, Sep 29, 2011 at 04:14:04PM +0200, Mattia R. wrote: > Hello, > > i have a block that takes 3 bytes of data in and output 4bytes of data (3:4). > > It’s possible to generate, sometimes, extra output? > > I mean, sometimes it take 3 bytes and output 5 bytes. It’s possible? How i tell > to the scheduler? That’s possible if you create a gr\_block and use the general\_work() function (so don’t derive from a sync\_interpolator). The general\_work() function lets you manually set how many bytes were consumed and how many were written to the output buffer. But you _must_ check the output buffer’s large enough. However, you sacrifice some performance and possibly some functionality of GNU Radio (e.g., IIRC, I don’t think you could propagate stream tags automatically through this kind of block). Perhaps re-thinking your signal flow is more optimal. ## MB Karlsruhe Institute of Technology (KIT) Communications Engineering Lab (CEL) Dipl.-Ing. Martin B. Research Associate Kaiserstraße 12 Building 05.01 76131 Karlsruhe Phone: +49 721 608-43790 Fax: +49 721 608-46071 www.cel.kit.edu KIT – University of the State of Baden-Württemberg and National Laboratory of the Helmholtz Association ---
**Author:** ![Mattia\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@Mattia\_R](https://www.ruby-forum.com/u/Mattia_R)\ **Post date:** [September 29, 2011, 6:05pm UTC](https://www.ruby-forum.com/t/c-block-that-generate-extra-data/212318/3 "2011-09-29T18:05:42Z")
Thank you for the reply. How can i reallocate the output buffer if is too small? Let’s assume that my block has an input itemsize of 3 byte and an output itemsize of 4 byte. Forecast with 1:1. If the scheduler keeps to give to my block only 4 bytes for output, how can i force to give me more? Thanks -----Messaggio originale----- From: Martin B. Sent: Thursday, September 29, 2011 4:20 PM To: removed\_email\_address@domain.invalid Subject: Re: [Discuss-gnuradio] C++ block that generate extra data * * * Discuss-gnuradio mailing list removed\_email\_address@domain.invalid [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) ---
**Author:** ![Mattia\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@Mattia\_R](https://www.ruby-forum.com/u/Mattia_R)\ **Post date:** [September 29, 2011, 6:57pm UTC](https://www.ruby-forum.com/t/c-block-that-generate-extra-data/212318/4 "2011-09-29T18:57:03Z")
I think you should tell it in the constructor. like this: #define NR\_OF\_WORDS\_ADDITIONALLY\_NEEDED 4 my\_usrp\_rx\_tx::my\_usrp\_rx\_tx(void) : gr\_block(“my\_usrp\_rx\_tx”, gr\_make\_io\_signature(1, 1, sizeof(short)), gr\_make\_io\_signature(1, 1, sizeof(short))) { set\_output\_multiple(NR\_OF\_WORDS\_ADDITIONALLY\_NEEDED); } Then in general work function, for example, you can increment “manually” 4 words before your out buffer will say “bang”. Patrik ----- Original Message ----- From: “Mattia R.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: “gnu radio” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Sent: Thursday, September 29, 2011 19:04 Subject: Re: [Discuss-gnuradio] C++ block that generate extra data