Re: [Discuss-gnuradio] fusb and select(2)

[Greg Troxel]

  As a die-hard old-school unix programmer, I want to be able to grab data
  from a USRP-like device, under control of a main loop based on
  select(2).  The comments in the source code of fusb are not encouraging.

The code to handle the USRP on NetBSD implements read/write/select
just like you'd expect.  The wrinkle is that you have to issue an
ioctl to put it in 'continuous read mode', and in that you give a
buffer size and the transfer size to do.

The other problem is that each direction is limited to 16 MB/s because
USB transfers aren't pipelined all the way to the hardware.  But
that's a bug to be fixed, not a design choice.

The code is in GNU Radio trunk from just before 3.0 (and thus in 3.0)
and has been in NetBSD-current since some time this summer.

All that said, Eric's comments about the future with time tagging are
certainly relevant.  It may be that some systems work like he
suggested, with a thread, and others have the kernel do it.  I suspect
that the issue of multiple readers can be separated from the
timeliness issues.



-- 

    Greg Troxel <address@hidden>

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