The ATSAME70 device series gives the user the option to reallocate the RAM section, usually starting at 0x20400000, to other memory areas as TCM memory. Per default the RAM section is one block ranging from 256 - 384 KiB in size (depending on which specific device is used).
To reallocate the RAM the so called General Purpose NVM Bits can be used. More information can be found in the corresponding family user guide.
This setting needs to be taken into account when linking your application in the IDE as not all available RAM is necessarily in one memory region.