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The RTC has an included 128-byte battery-backed NVRAM which can be accessed using tshwctl. Its contents will remain with the main power off, so long as the RTC battery is installed and withing a valid voltage range.

tshwctl --nvram

This will return a format such as:


This breaks up the NVRAM into 32 32-bit registers which can be accessed in bash. As this uses the name=value output, "eval" can be used for simple parsing:

eval `tshwctl --nvram`
echo $nvram2

From the above value, this would return 0x48ca4278. To set values, the respective environment variable name can be set:

nvram0=0x42 tshwctl --nvram

Note that the command 'tshwctl --nvram' will output the current contents of NVRAM before setting any new values. At this point, running 'tshwctl --nvram' once more will print the updated contents for verification. This can be used for reading a 32-bit quantity and updating it with a single command.