I want to save some data in sim memory as draft message and later read it. I am Using Arduino DUE and SIM800L Basically my main target is to keep in check the total uptime(approximate, error of upto 2-5 mins is acceptable) of my arduino and i am trying to achieve it something like this when ever it is powered on it will

Get current time using NTP after every several interval

Save it in SIM memory somehow as initiation time

Take next value after some interval and store it in next space and make it as final value

update final value every interval

store total time difference between initial and final value in a new space where uptime in this session is stored

next time when ever it restarts it will add total uptime value and uptime in this session value and then clear uptime in this session value for this current session

Now when ever that SIM receive any message in predefined format, It should send back the total uptime value on the number from where the message is received.

I don't want to use any external memory but found no way to use SIM's internal memory to store these values and save them from erasing on restart.

Any help will be appreciated

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