[atlas] Dead probes - slightly OT

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On 2015/10/28 17:50 , Gert Doering wrote:
> On Wed, Oct 28, 2015 at 05:30:49PM +0100, Wilfried Woeber wrote:
>> This seems to imply that the probes can bootstrap (off the 'net?)
>> without the USB stick present ? If this is the case, what is the
>> USB stick used for?
> 
> As far as I understand from the "firmware upgraded"-messages, the
> internal flash has some sort of immutable emergency recovery
> firmware on it, which is good enough to pull an upgrade from the
> master, install to USB stick, and reboot into it.  Or so.
> 
> And, for measurement data :-)

Close enough :-)

The tp-link comes with 4 MB flash. This not enough to store the
measurement code let alone also storing measurement results as well.
Worse, if a power failure happens at the wrong moment during an
upgrade of the internal flash then the tp-link is bricked.

So the architecture we came up with is that the tp-link boots from
internal flash and then either sets it root directory to the USB flash
stick and runs from that or if an 'empty' USB flash is detected,
downloads firmware from a controller and writes it to the flash.

This way, updating the code on the USB flash is completely safe. If
something goes wrong it is just a matter of asking the probe host to
perform the procedure to get the USB stick to be re-initialized.

We can and have updated the firmware on the built-in flash. But that's
quite rare and there is the risk that it may brick some probe.

Philip
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