Re: [Discuss-gnuradio] Random number of output items

[Francois Gervais]

Thanks Activecat you actually answered quite well to my question. I thought it might be better to send 0s, i'm glad you confirmed that. And thanks for the output algorithm.

Could you tell me more about forecast? Most of the time I need 8 input samples to produce one byte output so I set the forecast like so:

ninput_items_required[0] = noutput_items*8;

It seems pretty straight forward. Is this correct?

On Mon, May 19, 2014 at 9:32 PM, Activecat <address@hidden> wrote:

On Tue, May 20, 2014 at 2:17 AM, Francois Gervais <address@hidden> wrote:

Hi,

I'm making a block which takes bit from a bit slicer and output packets as input comes in. My block will output bytes so it can emulate a usb adapter that receives the RF signal and output a packet stream through an FTDI. That way I can use the stack that comes with the adapter without owning one. I'll use a FIFO file so other than not issuing the serail configuration the stack should be used pretty much as is.

However, I'm not sure what I should do about the the number of outputs. Let say I'm waiting for the preamble, I won't output anything. When I get the preamble and the sync I'll send a sync byte of my own. From here every 8 inputs I'll output a byte. So basically my block will output 0 or 1 output.

Can someone help me a little with the use of forecast and noutput_items in my case? Also do I need to use the consume_each function?

If your block emulates a USB adapter, defines it as a source block, then you don't need to touch forecast().

If your block takes input from another block, then it is not source block.

I don't really understand your requirements.

The number of outputs (referred as noutput_items) is determined by the scheduler, not yourself.

Says, when you have X bytes to send out,

    if X > noutput_items:  Send out noutput_items number of output, and return noutput_items

    if X < noutput_items:  Send out X number of output, and return X

    if X == noutput_items: (either one of above)

When you send out a sync byte, add that to the output count.

When you are waiting for the preamble, you may want to send out a series of zeros, rather than just producing no output. 

Producing no output may cause the downstream blocks to become unresponsive.

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