Re: [Discuss-gnuradio] MSB

[Davide Anastasia]

Il giorno gio, 15/03/2007 alle 12.17 -0700, Eric Blossom ha scritto:
> I think you'll find it easier to do the unpacking in a separate block
> downstream from the usrp1_source_s.  Modifying usrp1_source* to handle
> samples smaller than 1 byte is going to take quite a bit of work.
> Part of the problem is that the code is written in terms of functions
> such as sizeof_basic_sample() which returns a size in bytes.  In your
> case,your basic sample is smaller than a byte.  The current code
> doesn't know how to deal with that.

I can use the "format()" function to obtain the width of the sample.
Actually I'm using this way:

  case 1:
    for (int i = 0; i < nitems; i++){
        switch ( format() ) {
                case 1:
                out[i] = usrp_to_host_short(s16[i]);
                // temp = 0 | s8[i] << 8;
                // i++;
                // out[i] = temp | s8[i];       // Si può fare?
                break;
                case 2:         
                out[i] = s8[i] << 14;
                break;
                case 4:         
                out[i] = s8[i] << 12;
                break;
                case 8:
                default:
                out[i] = s8[i] << 8;
        }
    }
    break;

I change sizeof_basic_sample() in order to return 1 with samples smaller
than a byte. I written a little C++ program to obtain from a 1 bit
stream a table (#, value{0 or 1}). I think it can been reused to create
a module, which take a stream and return a 16 bit sample per bit.
> 
> After unpacking, what representation do you want for your samples?

I guess a simple continuos stream of bit is enough.
> 
> If bytes containing 1-bit per byte are OK, then perhaps the easiest
> approach is to create a gr_packed_to_unpacked_sb.*
> 
> You should be able to do this by changing:
> 
> # other blocks
> others = (
>     ('gr_chunks_to_symbols_XX',     ('bf', 'bc', 'sf', 'sc', 'if',
> 'ic')),
>     ('gr_unpacked_to_packed_XX',    ('bb','ss','ii')),
>     ('gr_packed_to_unpacked_XX',    ('bb','ss','ii'))
>     )
> 
> 
> to
> 
> # other blocks
> others = (
>     ('gr_chunks_to_symbols_XX',     ('bf', 'bc', 'sf', 'sc', 'if',
> 'ic')),
>     ('gr_unpacked_to_packed_XX',    ('bb','ss','ii')),
>     ('gr_packed_to_unpacked_XX',    ('bb','ss','ii', 'sb'))
>     )
> 
> in gnuradio-core/src/lib/gengen/generate_common.py

"b" stays for byte or bit?
> 
> On the other hand, I assume that ultimately these end up as some kind
> of complex data type, so perhaps some other kind of mapping to
> gr_complex would be useful.
-- 
Davide Anastasia

web: http://www.davideanastasia.com/
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