```
#if IEEE_ADDR_CONF_USE_SECONDARY_LOCATION
#define IEEE_ADDR_LOCATION IEEE_ADDR_LOCATION_SECONDARY
#else 
#define IEEE_ADDR_LOCATION IEEE_ADDR_LOCATION_PRIMARY
#endif
```
and then
`dst[i] = ((uint8_t *)IEEE_ADDR_LOCATION)[len - 1 - i];`