Date: Tue, 15 Feb 2011 18:35:19 -0500
From: Patrick Allison <barawn@pandj.org>

[items regarding shutdown]

Right now, the SBC can shut off any daughterboard, the GPS, and the
FPGA+clock multiplier. It can't shut off the USB microcontroller or
the CSAC Rb clock. (An external Rb clock could be shut off if there
was a little I2C "support board" for it). If we want to add the
ability to kill power to basically everything, we would need to
basically implement some little interface to the Vicor DC-DC boards
(although not the 12V supply used for the SBC, obviously) and maybe
use the GPIOs on the SBC.

The other possibility is to take the SMBus (an I2C compatible 2-wire
interface) on the SBC's daughterboard connector and put a connector
for it on the ATRI board (so it's just straight wiring, no power/etc.)
- maybe SDL, maybe something else just so that it looks different from
the other connectors. Then, inside the DC-DC box, we put maybe a
temperature sensor, ADC, and a GPIO 4-port expander (e.g. the MAX7323)
and connect the SBC's SMBus to that.

Then the SBC can basically shut everything off if it wants to (except
it's own power, obviously) and in addition, we can monitor voltages
and temperature in the DC-DC box.

So, first question:
1) Should I just add something like another hot-swap controller for
the CSAC Rb clock option so that the SBC can shut down *just* the Rb
clock if needed? (If this makes sense, it'd probably also make sense
for me to route the GPS's PPS output to the FPGA as well).
2) Should I put the SBC's SMBus interface on a connector as well? That
would give us an "external" option independent of the ATRI board other
than the GPIOs such that we could put some monitoring in the DC-DC
box. This is probably a good thing in general.

Patrick