We talked about how to record data. A MicroSD card is too large for a ring, obviously. However, a uSD card is good because it contains a controller that takes care of things like mapping bad memory sectors and doing load leveling. It’s not clear to me whether or not these functions need to be performed with a discrete flash memory IC.
Here is an SPI-connectable 1G-bit flash chip from Micron that is only 6mm x 8mm:
This device has 4 stacked 256 M-bit die. The memory is therefore arranged as 256Mbx4, or 128 M-Bytes.
I am hoping that this device could be used both for data storage and program storage. For example, if the Dialog DA14580 were used, the program could be loaded from the memory device to the 42kB system RAM.
If there were swapping involved that would most likely kill the power budget. After development is completed the OTP memory of the DA14580 could be used. Maybe an OTP memory saves some power.
Writing data to a flash memory takes a lot of power. Maybe it’s not practical to consider it. Adesto 32Mbit memory, 6mm x 6mm BGA: http://www.adestotech.com/sites/default/files/datasheets/doc3686.pdf