[hpsdr] ALEX - Call for comments

[Steven Wilson]

Lyle Johnson wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hello Graham!
>
>   > A block diagram of Alex and other information is on the Wiki.
>   
>> The current plan is to use an I2C I/O expander chip to control
>> the RF switches, not the full CPLD bus interface as shown.
>>     
>
> Hmm, is it possible to also include SPI as an alternative selection 
> method?  Looking ahead to Sasquatch, and not sure how the mix of SPI and 
> I2C peripheral pins will work out, so I'd like to have both options if 
> feasible.  SPI is very easy to implement in a CPLD or FPGA, and requires 
> few resources.
>   
Lyle,

I'm working on the I2C Slave design for the Epi board -which will also
have an I2C master to allow non-polled interrupts like button pushes to
be sent to Ozy.   It's tied to the I2C slave by a Wishbone bus interface
- let's us drive other OpenCores designs more easily.  One big reason
for staying with I2C connectivity is we can use the same two wires for
ALL boards as a party line interrupt system.

The BIG problem with the SPI interface I see is the fact that you have
to have a Chip select for each slave on the SPI bus.  I2C uses an
addressing scheme  to do the connectivity. IOn the other end of things
SPI is potentially ALOT faster.

It IS conceivable to mix a SPI and I2C slave in a single design - we
just haven't implemented something like that yet. 

73 de Steve KA6S


>
> Thanks for taking this on, Graham, and welcome aboard!
>
> 73,
>
> Lyle KK7P
>
>
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