On Tue, 2010-02-16 at 14:42 -0500, George Nychis wrote:
> Hi Eric,
>
> Sorry for the late response here, I've been wrapped up in so many
> things.
>
> Is your latest compiled RBF in your developer branch? There are
> several people I know (some that I CC'ed) that are interested in using
> the inband code.
>
> Last I checked, the timestamp had an issue of "jumping" which I know
> you tried to fix. Last time I tried your branch, I'm not sure it was
> working yet. Have you confirmed that timestamps to the host are not
> jumping in any manner when there is no overrun, and have you confirmed
> that timestamps are being treated properly when trying to transmit?
>
> Thanks a bunch for updating this code.
>
> - George
>
>
> On Tue, Jan 26, 2010 at 5:32 AM, Per Zetterberg
> <
address@hidden> wrote:
>
> Eric Schneider wrote:
> Hi all, I'm looking to be doing some more rework of
> the USRP1 inband
> code, specifically to align with the USRP2 VRT work.
>
> For those not familiar, USRP1 inband allows for
> timestamped rx/tx
> samples (and commands), which is very useful for TDMA
> type systems. It
> is a separate FPGA configuration and host side
> interface.
> Has anyone besides me used the current inband FPGA?
>
> I'm not sure who on this list is interested in such a
> thing, but if you
> have specific needs you want addressed, speak up now!
>
> A few notes on my current thinking:
>
> 1. I do not intent to implement VRT over USB. Only to
> implement a VRT
> compatible interface on the host. The USB inband
> protocol will simply
> serve to make that possible in the most efficient way
> possible.
>
> 2. I don't intend to keep the existing inband packet
> structure. This is
> one area where interested parties really need to
> provide feedback as to
> supported (or supportable) feature sets.
>
> It is my hope that the new inband Verilog modules can
> be used by other
> custom FPGA builds as a standard host interface.
>
> For example, it has just recently occurred to me that
> the FPGA side
> could be made more efficient by the use of trailer
> metadata rather than
> headers. Since the USB packets are fixed size, I
> don't really see a
> downside.
>
> There are also fields in the current inband packet
> that are either
> obsolete, or should be optional fields, IMO. RSSI,
> for example.
>
> Do timestamps really need to be 32 bits? That allows
> scheduling
> transmission 33 seconds in advance on a 64MHz clock,
> which seems
> excessive to me.
>
> Is there a reason to send timestamps in every packet
> if samples are
> contiguous?
>
> I'm leaning towards a 16 or 32 bit trailer with
> optional, per packet,
> meta data. Less than 16 bit alignment of trailer/meta
> would fragment
> individual (16 bit) samples, and 32 bits would keep
> I/Q interleaving
> order constant between packets. I am open to
> entertaining the idea of
> tiny (8 bit?) trailers, so long as we can reliably
> detect and recover
> from buffer overruns and such.
>
> --ETS
>
>
>
>
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>
> Sounds great!!
>
> It would also be nice to have a "pps" input to synchronize the
> clocks of multiple units. General purpose pins could be used.
>
> One feature I have always wished for is "external triggering"
> where a USRP transmits/receives when a pin goes high. But that
> is maybe another project.
>
> Good luck!
>
> BR/
> Per
>
>
>
>
>
>
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