Thanks.  I saw notes that seem to indicate that option. Anyone at Ettus/NI care 
to chime in as to how to do it?  I found an example for E320 that shows an 
RFNoC .yml with a dram FIFO.  I could make one for N320, but it is not clear 
how to use it from gnuradio.
________________________________
From: Rob Kossler <[email protected]>
Sent: Tuesday, January 27, 2026 6:45 AM
To: Eugene Grayver <[email protected]>
Cc: usrp-users <[email protected]>
Subject: [EXTERNAL] Re: [USRP-users] TX DRAM buffer


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Hi Eugene,
I "think" that the replay block can act as a FIFO in recent UHD images.  But, 
there is a possibility I am wrong such that there is a build-time parameter 
that is needed to config this.  Another option would be DPDK if you are not 
already using it.
Rob

On Mon, Jan 26, 2026 at 7:00 PM Eugene Grayver 
<[email protected]<mailto:[email protected]>> wrote:
Hi,

The default TX buffer for N32x is 128k samples = 512 kB.  The box has 1 GB of 
DRAM.  I am getting occasional underflows when streaming at 200 Msps, even 
though the CPU is not very loaded and easily meets the average throughput.

I have done all the usual stuff — isolated cores, pin threads to cores, etc.

Is there a way to increase the default DRAM buffer size w/out rebuilding the 
FPGA image?

Thanks.

Eugene Grayver, Ph.D.
Principal Engineer
310-336-1274
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