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Re: [Discuss-gnuradio] Latest USRP2 firmware binaries updated

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Latest USRP2 firmware binaries updated
Date: Wed, 3 Mar 2010 09:58:52 -0800

On Tue, Mar 2, 2010 at 23:28, Firas Abbas <address@hidden> wrote:

> I think USRP2 has a big (1 MByte) external static RAM.

Yes, it does.  But that's not where the embedded microprocessor
instruction store is located.  The aeMB reads instructions out of a
32K block ram inside the FPGA itself.

It may be possible to use the SRAM as the code store and the block RAM
as an I-cache, but that's a fairly significant amount of FPGA design
work/modification, and cache-miss performance might be too slow.

In any case, about 25% of code in the firmware (txrx.bin) is combined
daughterboard management, like tuning control parameter calculation,
etc.  By breaking these out into individual images, most of that space
is freed up for other things.  Another option would have been to
implement overlays, where the required daughterboard code is loaded
into a common place in memory from the SD card after the unit detects
which daughterboard is installed.

There are other opportunities for improving the code size of the other
75%.  It seems the Microblaze gcc port, at least the version we're
using, is not that efficient at code generation.

Patches always welcome :-)


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