Every device (client) should have a memory topics. Memory topics gives possibility to store some user data in device, and device can freely change this memory on the run. But unlike, registers, memory doesn't have a notification on each change, and could be read only by external command. Another difference with registers that there is only one linear memory space and user/device should map according to the usage.
There are only two topics inside:
read - Read device memory. Command have two parameters separated by ; - [addr];[size]. Response will have format - [size];[data]write - Write device memory. Format - [addr];[data] . Response will have format: - [addr];[size]This topics uses base64 to encode the data
Check examples in Topic 'read' and Topic 'write'