Part Number: MSP430FR2433
Here I offer my experience trying to understand the documentation for backup memory.
SLAU445h (family user guide) says "Configurable from 32 bytes to 256 bytes". It should say something like "each device in the family has a different number of backup memory locations." IMO there is no end-user action to "configure" the memory.
SLAU445h also documents only two registers, BAKMEM0 and BAKMEM1. IMO these are just examples. Each device will have a different number of registers. The registers do not "control" anything, they are just memory locations that can be read and written. The document could just say that, and use one example register e.g. "BAKMEMx"
SLASE59B (datasheet for MSP430FR2433) says "This device provides up to 32 bytes that are retained during LPM3.5." IMO it should say "provides exactly 32 bytes". It could also say "in 16 named word locations."
Also, as discussed in the linked thread, it is not clear why one would want to use backup memory instead of FRAM. The documentation could say that one reason is: to dynamically write FRAM, you must first disable VMA NMI upon writing to FRAM. That is, you can always write to backup memory, but a write to FRAM will trigger a VMA NMI unless that has been disabled.
Also, the linked thread confuses the issue whether FRAM is unpowered with whether FRAM contents are lost during LPM4.5. In that thread, a TI employee says "The difference between FRAM and backup memory is that the latter is retained during LPM3.5." Table 6-1 is cited, and that table shows that FRAM is "off" during LPM3.5 (and other modes) but that only means FRAM is unpowered, not that FRAM contents are lost through LPM3.5.
The reason I was looking at the documentation, I was exploring whether I needed to disable backup memory to enter LPM4.5, using some sort of control register. The documentation could say "power to backup memory is automatic, determined by the LPM mode."
I could be wrong. To summarize, I think a paragraph or two of explanation in the family user's guide would help.
