[hpsdr] FX2 / I2C multi-master

[Eric Blossom]

On Wed, Mar 15, 2006 at 12:44:18PM -0800, Christopher T. Day wrote:
> Eric,
> 
> I am slogging though the USB spec [I actually _like_ reading specs,
> another moral failing on my part] and the FX2 spec, but they are a
> trifle long. However, it seems that that is exactly the design point of
> the FX2.

I found Chapter 9 "USB Device Framework" of the usb 2.0 spec the most
relevant to building a peripheral.

> Interesting about the USRP experience. I wonder about the "*can't*
> control the stuff" comment. Isn't I2C multi-master? Couldn't the FPGA
> also fiddle the chips? Note that that is strictly a technical question.

You're right it could.  The FX2 drives SCL with on open-drain pin.

> Believe me, I _know_ multi-master complicates the situation enormously,
> kills off the FPGA space saving and is generally probably not a good
> idea in this case. Just wondering if it's technically possible, that's
> all.

I think it is possible modulo arbitration.  Also, I think you can
build a I2C master in about a 100 LE's, so I wouldn't sweat the
resource consumption.

> Clearly, I need to work though the use cases for chip control and
> interaction some more.

Always a good plan ;)

Eric, K7GNU

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