Re: [Discuss-gnuradio] HDLC framer

[Marcus Müller]

Thank you, Nick, for clarification!
Yes, I was kind of messing that up.

I've done little PMT work -- is there a convenient way to "reinterpret"
the payload of any PMT as u8v/blob?

Greetings,
Marcus

On 12/04/2014 06:01 PM, Nick Foster wrote:
> I wrote the HDLC framer to use PMT blobs (specifically, PMT pairs with a
> length field and a blob) because it seemed that was the convention we were
> settling upon in GR to handle binary messages. I'm unaware if there was any
> formal specification or agreement to this format.
>
> To clarify, the missing feature is just dealing with blobs that aren't a
> multiple of 8 bits in length. To do so would probably require changing the
> length field to represent nbits instead of nbytes, and using a padding
> convention (msbit or lsbit) to determine which bits in the last byte of the
> blob should be included.
>
> I haven't seen too many (len%8) HDLC frames out there so I never got down
> to putting that in there. The deframer would also have to be modified,
> specifically crc_ccitt().
>
> --n
>
> On Thu, Dec 4, 2014 at 8:25 AM, Marcus Müller <address@hidden>
> wrote:
>
>> Hi Daniel,
>> the HDLC framer can only deal with messages containing PMTs that are
>> "blobs", ie. u8vectors.
>> In fact, that's a missing feature:
>>         pmt::pmt_t len(pmt::car(msg)); //TODO for non-mult-8 nbits
>>         pmt::pmt_t blob(pmt::cdr(msg));
>>         if(!pmt::is_blob(blob))
>>             throw std::runtime_error("HDLC framer: PMT must be blob");
>>
>> Instead of making a pmt.intern("String"), you will need to have a
>> u8vector. It's a bit ugly to generate that in single line:
>>
>> pmt.pmt_to_python.numpy_to_uvector(numpy.array([ord(c) for c in "Hello
>> World"], numpy.uint8))
>>
>> you might need to add an "import block" that does an "import numpy".
>>
>> Greetings,
>> Marcus
>>
>> On 12/04/2014 11:52 AM, Daniel Batista wrote:
>>> Thank you Marcus,
>>> I try the following:
>>> MessageStrobe("Hello World") ----> HDCL framer ---->HDLC deframer ---->
>> Message Debug
>>> and I get the following error message:thread[thread-per-block[2]: <block
>> hdlc_framer_pb (1)>]: pmt_car: wrong_type : Hello World!
>>> What did I do wrong?
>>> Daniel
>>>
>>>
>>>
>>>      On Wednesday, December 3, 2014 10:55 AM, Marcus Müller <
>> address@hidden> wrote:
>>>
>>>  Hi Daniel,
>>>
>>> PMT is short for "polymorphic type" [1].
>>> GNU Radio uses PMTs for stream tags and, more importantly here, for
>>> asynchronous message ports.
>>> So the idea is that you have a source of messages[2], sending your
>>> data to the HDLC framer, which frames it and generates output items.
>>> If you want some illustrated guide through these concept, I'd
>>> recommend the new guided tutorials on gnuradio.org[3] numbers 1 through
>> 5.
>>> Greetings, and happy hacking,
>>> Marcus
>>>
>>> [1] http://gnuradio.org/doc/doxygen/page_pmt.html
>>> [2] http://gnuradio.org/doc/doxygen/page_msg_passing.html
>>> [3] http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorials
>>>
>>> On 12/02/2014 10:47 AM, Daniel Batista wrote:
>>>> Hi, I read in the documentation that HDLC framer takes in PMT
>>>> binary blobs and outputs HDLC frames as unpacked bits.I don't
>>>> undestand what are the PMT binary blobs.How can I put in an HDLC
>>>> frame a "Hello World" message? ThanksDaniel
>>>>
>>>>
>>>>
>>>>
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