Plan for 10/100 Ethernet support for umTRX

Robin Coxe coxe at
Fri Jul 27 14:27:02 UTC 2012

Hi Sylvain.

On Fri, Jul 27, 2012 at 9:04 AM, Sylvain Munaut <246tnt at> wrote:
> Hi,
>> The Ettus UHD framework adopted for the umTRX only supports GigE
>> (simple_gemac).   A reworked, Wishbone-compliant 10/100 Ethernet MAC
>> is included in the OpenRISC SoC project on Opencores.  It has been
>> ported to the Digilent Atlys board, which has a Spartan-6 FPGA.
>> I'll begin the port of this Ethernet MAC (a cleaned-up version of the
>> 10/100 core on OpenCores) to the UmTRX and test it on Close-Haul's
>> SP-605 Spartan-6 eval. board.   I'm not quite sure how long this task
>> will take, but this feature falls into the
>> "nice-to-have-but-not-urgent" category.
> But would it be 10/100/1000 ? or just 10/100 ?

Just 10/100.   User would choose GigE or 10/100 via an IFDEF in the
Verilog.    I suppose it would also be possible to multiplex in the
simple_gemac with this 10/100 core and set the mode from the ZPU via
the Wishbone interface.  There is a tri-mode Ethernet MAC that Ettus
used to use on the USRP2, but I've never been able to make much sense
of it.   If you have suggestions for a better way to add 10/100
support, I'm definitely interested in hearing them.

> Also, doesn't UHD make use of the 'wait' feature of Gigabit (i.e.
> PAUSE frames / flow control ) to avoid loosing data ? This doesn't
> exist on 10/100 IIRC.

I'm not all that familiar with UHD, so you probably know better than I
do.  Perhaps Thomas could comment?


Robin Coxe  |  Close-Haul Communications, Inc.  |  Boston, MA

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