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Re: [Discuss-gnuradio] Using the MIMO port for serial comm. to a Virtex

From: Charles Irick
Subject: Re: [Discuss-gnuradio] Using the MIMO port for serial comm. to a Virtex5 board
Date: Mon, 7 Dec 2009 14:57:01 -0500

Thank you for the fast reply. It looks like I need the SATA fanout
connectors to be the host in this case because pin 2-3 are TX for the
SATA port. Would there be any issue having the mini-SAS as the target?
(part: iSAS-7P88-U)


On Mon, Dec 7, 2009 at 2:29 PM, Matt Ettus <address@hidden> wrote:
> On 12/07/2009 11:17 AM, Charles Irick wrote:
>> Hello,
>> I am narrowing down my issues and I think my problem is related to
>> physically connecting the USRP2 to the V5 and it being a host to host
>> connection. (I think I have Tx connected to Tx and Rx to Rx) For
>> verification, are the A1-A13 pins on top or the B1-B13 pins for the
>> mini-SAS port? (
>> http://gnuradio.org/trac/attachment/wiki/USRP2Schem/expansion.pdf ) My
>> guess is that the B1-B13 pins are at the top with B1 being in the top
>> left corner if you are looking at the port on the front of the USRP2.
> All outputs are on B, which is on top.
>> Also, when using two USRP2s you should have this same host to host
>> issue, is this resolved because the mimo cable is a crossover? Thanks
>> in advance for any help.
> All SAS cables are what you would call crossover.  A on one side connects to
> B on the other.  Wiring diagrams are here:
> http://www.cs-electronics.com/isas-cables-NEW.htm
>> Charles
>> On Tue, Dec 1, 2009 at 4:30 PM, Matt Ettus<address@hidden>  wrote:
>>> On 12/01/2009 12:58 PM, Charles Irick wrote:
>>>> Hello,
>>>> I'm most likely having a clock issue because I cannot get any data
>>>> transfers going between the USRP2 and GTPs on the V5. A few questions:
>>>> - I'm not quite sure I understand the 10MHz reference clock idea, or
>>>> its usage; I looked through the HDL and everything on the FPGA is
>>>> running at 100MHz.
>>> The 10 MHz reference input on the front is optional.  If you connect it
>>> and
>>> enable locking, the 100 MHz main oscillator will lock to it, otherwise it
>>> will free run.  Everything inside the FPGA runs at 100 MHz (DSP) or 50
>>> MHz
>>> (processor).
>>> There is also a 10 MHz reference clock sent out on the MIMO connector.
>>> When
>>> turned on, it will be the 100 MHz clock divided down by 10.
>>>> - I assume I will not need to provide this reference clock if the
>>>> USRP2 is the driver given that sd_gentest appears to do so in the main
>>>> functions clocks_mimo_config. Either way I'm using the SAS to quad
>>>> SATA cable so the clock isn't even transferred to the GTPs (literally,
>>>> it's supposed to derive it from the data).
>>> sd_gentest will generate packets and send them on the serdes on the MIMO
>>> cable.  You should be able to receive it without using the 10 MHz
>>> reference
>>> clock because, as you say, the clock is recovered from the data.
>>>> - My only clocking options on the GTP's are 150 or 75MHz. I'm not sure
>>>> if I should clock the USRP2's FPGA or the reference differently to
>>>> match this.
>>> The important thing is that you get the GTPs set up for the correct data
>>> rate.  On the USRP2, the main clock to the SERDES chip is 100 MHz.  2
>>> Bytes
>>> are sent on each clock, so the effective data rate is 1.6 Gbps. However,
>>> since 8b-10b coding is used, the on the wire bit rate is 2.0 Gbps
>>> (20*100MHz).  So whatever reference clock you use, you need the GTP to be
>>> working at 2 Gbps.  I am by no means an expert on the GTPs, but I think
>>> the
>>> easiest way to do this is to have a reference clock of 100 MHz.
>>> You could probably use the PLLs in the V5 to create a 100 MHz reference
>>> clock from one of your other clock rates.
>>> Matt

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