What HVRAM locations of the Si4010 are used by the API?
There are two API functions that write the HVRAM (beside vHvram_Write):
a. Clears the HVRAM.
b. Initializes the HVRAM byte at address 0x02 to 0xFF.
It happens only when battery was inserted, so this location can be used by the user code for any purpose.
Clears bit in HVRAM which means "chip didn't shut down correctly."(bit 0 at address 0x00)
If user wants to use this bit to check if shutdown was called, it has to be set by user code.
Conclusion: The whole HVRAM except the first bit can be used freely by the user code.