Yes I use an Olimex A20. It has no RTC and there is an external module posible. Now I use NTP for the time. There is also a way to use the GPS
time. I found the sources for that already. What I have not yet figured out is if this will occupy the gps and if it can still be shared with OpenCPN.
The A20 including a 4 port usb serial converter and an old gps dongle uses 3.6W if it is very busy.
I did try to get SDR running on it with a gui but that became too slow or too unstable. So for now I ditched that idea.
Sending an SD card to Trinidad would not be needed. If the person there has a fingerprint software
where he can readout the 32bit serial number. That number can be send to the seller of the maps to encode them to that number.
Ok the hole in that is that I could emulate a SD card with some external piece of software
. And generate any serial I want. Or use an fpga. But if I want to put so much effort in breaking it nothing will stop me.
Would using the MAC address be an idea?
Combine the ARM CPUID with the ID of the SD card or MAC address. That would make a unique number for that system.
I did not find a generic way of getting a unique serial from ARM.
Oh boy devising software protection that goes against everyting I stand for. Some day I will hate my self for this...