Subject: Re: ugen change for review (try 2)
To: Hans Petter Selasky <>
From: Greg Troxel <>
List: tech-kern
Date: 07/21/2006 13:46:20
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Hans Petter Selasky <> writes:

> Does your USB device send short packets, so that you get short transfers?

No, the USRP only sends full-sized packets.

> What buffer size do you use?

We've tried various buffer sizes, from 128KB to 2MB.

> I would suggest enabling your change by default, and no IOCTL's to
> enable it,

As I explained to Berndt, that would change the semantics of ugen(4).

> but I would rather use a block buffer, than a ring buffer. That way
> it is possible to pass short packets to the user application. With a
> ring buffer, short packets get lost, which sometimes are important
> for synchronization.
> I am planning a change similiar to yours on FreeBSD, but I have not had t=
> to do it. What I have done so far is to implement a block buffer system:

Are you trying to preserve the packet boundaries?  We are explicitly
not worrying about that, since a) those currently have no semantic
significance with the USRP and b) it's all full-sized packets, so
alignment is maintained.

> When it comes to the IOCTL name, I would prefer something like:=20

The ioctl sets both buffer size and the size of the transaction passed
to the lower layers, and those names don't convey that.

    Greg Troxel <>

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