[Discuss-gnuradio] A few questions about subclassing gr_block

[Mark Cottrell]

Hello,

I am trying to create a block that detects sync patterns at baseband tagging the first sample of the pattern using stream tags, then using the tags down stream as part of demodulation.  I have made a few assumptions about how gnuradio works that I would like to validate:

- a sync pattern could span two blocks of samples passed to general_work

- I need to keep SYNC_PATTERN_LENGTH - 1 samples to get around this, so I should be able to use a general block and not output all of the items

- you can't tag historic samples (i.e. samples obtained using set_history), so I can't use that

are these all reasonable?

Currently I have an implementation of the block, but I am having trouble understanding the relationship between ninput_items and noutput_items.  When I feed the block from a file source consisting of 720 samples, I get ninput_items[0] = 720 and noutput_items = 512.  Does this value for noutput_items mean I can only consume and copy 512 of the input samples?  And do I need to implement forecast if I want to output more?

Thanks in advance for any help,

Mark

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