RMT driver, memory management clarification / documentation (IDFGH-12068)

[higaski]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

General issue report

The new RMT transmission driver introduced with ESP-IDF 5 does require the user to keep data pointed to by the transaction queue alive until this particular transmission gets completed. The documentation mentions multiple times that the internal queue really is just a job queue, but I still think that there should be one paragraph about memory management.

The potential to introduce very subtle bugs here is huge, specially when changing the RMT configuration. Imagine users switching from blocking to non-blocking behavior, or simply change the transaction queue size from 1 to 2.