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Re: [Discuss-gnuradio] UHD's recv_frame_size for E100

From: Michael Dev
Subject: Re: [Discuss-gnuradio] UHD's recv_frame_size for E100
Date: Mon, 25 Apr 2011 18:34:27 -0700

Yes, improved latency with smaller frame size is what I'm looking for.  506 samples of buffering is pretty big for me.  Also, being able to adjust the frame size to a nice size for my app would mean I don't have to have some additional buffering code (and the code to 'manufacture' rx timestamps for fragments that don't come with timestamps) between the recv() call and feeding the result to my app. 
On Mon, Apr 25, 2011 at 6:08 PM, Josh Blum <address@hidden> wrote:

On 04/25/2011 06:01 PM, Philip Balister wrote:
> On 04/25/2011 08:28 PM, Michael Dev wrote:
>> Unlike USRP1 over USB, it seems specifying the recv_frame_size on "args"
>> doesn't have any effect on E100.  I see get_max_recv_samps_per_packet()
>> always returning 506 and I see fragmented segements from recv() calls.
>> Is it
>> unadjustable for E100 or am I doing something wrong here?
> Due to the design of the fpga interface, the largest transfer between
> the fpga and gpp is 2048 bytes. Beyond this, Josh will need to comment :)

I didnt put in the hooks to change the frame size. It should be possible
without too much fuss. Right now, the frame size defaults to the maximum
size of the kernel ring buffer frames, or optimized for bandwidth. This
hook would allow you to make the frames smaller (optimized for latency).
Is that what you are looking for?


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