[hpsdr] GIBRALTAR LO generation question

[Lyle Johnson]

Hello Rick!

> That sounds OK.  Should it be a differential signal?

No, we're not set up for differential on the backplane.  We need to 
define an Atlas bus line for this, and the signal should be one that we 
can tri-state in case we need to use the bus line for another purpose.

One possible line is pin A24, signal name X22C6.  This is normally the 
JTAG clock "TCK" but this is typically only used during configuration. 
By tri-stating it normally, and only enabling it on command, we get 
re-use of the line.

Another possibility is pin A17, signal X15B7.  This one has no alternate 
use defined yet.  It also allows us to use the JTAG port to enable or 
disable the 10 MHz clock signal without contention.

I'm not sure what sort of command interface you envision for Gibraltar. 
  If it is going to hang on the I2C or SPI bus for control, then the 
JTAG re-use has some appeal.

Or maybe we can have both possibilities, by command?

73,

Lyle KK7P


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