Persistent circular buffer with CC3220SF
A typical external serial NOR flash would allow individual bytes to be written, but must be erased in 4K chunks.  If all you need is a single rolling buffer, a simple approach would use a page-status byte on each page to keep track of where data should go.  At any given time, there would be three "special" pages:


The current page, to which new data would be written.
The garbage page, which would be the one after that (or first page if the current is the very last one), which might contain anything, but whose contents should be presumed meaningless and thus ignored.
The tagged page, which would be the one after that (wrapping as above), and will be the only page (other than the garbage page, which could contain anything) where the page-status byte is programmed.


If there's room in the current page to add data, append there.  Otherwise, erase the garbage page, and program the page-mode byte on the page following the tagged page, turning that page into the tagged page, the previous tagged page into the garbage page, and the previous garbage page into the current page.

The tagged page may be identified because it will be the only page whose tag byte is programmed, but whose successor's tag byte isn't.  Note that the tag byte on the garbage page might read as be programmed, but its successor's tag byte will also be programmed.