Re: [Discuss-gnuradio] host format versus device format

[Martin Braun]

On 23.09.2015 11:44, Jason Matusiak wrote:
> For some reason I got myself wrapped around the axle with what is going
> on with the host and device format options.  For instance, if I look at
> the RFNoC Radio block, it has a host format with the options: complex
> float32, complex int16, and vita word32, and a device format of complex
> int16 (with no other options).
> 
> The way I understand things, the host format is basically the wire
> connection between blocks.  So complex float32 is I/Q with 4B for each
> in float format (so 8B per sample), and complex int16 is 2B on int for
> I/Q (4B per sample).  Am I still OK?  If so, I am failing to understand
> the device format option...
> 
> Although, all that said, as I look at a USRP Source block, it uses the
> term "output type" (which is analogous to the host format) and a "wire
> format" which I am guessing is the same as the "device format"  If that
> is correct, that means I don't have any idea what that wire is doing (as
> I would have mentally thought that the output type is the "wire").
> 
> I tried looking for some documentation on this but came up empty (though
> I am sure it is out there somewhere).

Good point about lacking info. Here's the gist of it:

- When data goes from device -> host, it uses the wire format (or otw
format)
- On the host, it gets converted to the host format inside UHD.
- Currently, all FPGA blocks use integer formats, on the X300, it's
always sc16
- In RFNoC, things become ambiguous. If you connect rfnoc block -> rfnoc
block, you never use the host format, even if it's set. If you connect
rfnoc block -> host, you convert to host format on the host. Downstream
GNU Radio blocks will thus use host format.

Not sure if this answers all your questions, but please come back if you
have any more!

Cheers,
Martin