i'm curious what kinds of applications you've found fram most useful for. it seems like a really cool technology, but the price point is so high that i struggle to understand when you'd use it rather than a combination of sram (or psram) and nand
probably so, but crote was talking about external fram chips
the msp430fr4132 you linked costs 160¢ in quantity 35, which is actually considerably cheaper than comparable flash-based chips like the msp430f233 https://www.digikey.com/en/products/detail/texas-instruments... which is 500¢ in quantity 25. so that's maybe one reason people would use fram: evidently it's cheaper than nor? but i'm pretty sure there are μcs with 8k of nor flash that are cheaper than that and in fact cheaper than the price difference. is this pricing policy some sort of loss leader by ti to drive fram adoption? it seems unlikely. does using fram instead of nor make it cheaper for ti to make the chip? surely 8k of nor couldn't account for such a large cost
on further investigation, i don't find μcs with 8k of nor flash that are cheaper than that, at least in stock at digi-key and still in production. https://www.digikey.com/en/products/filter/embedded/microcon... is the link to my search, which i trust hn will abbreviate in a useful way. but lcsc has the ch32v203 in stock for 39¢ in quantity 100 https://www.lcsc.com/product-detail/Microcontroller-Units-MC... and that has 20k of sram, 64k of flash (presumably nor!), and 24 gpios. that's half the gpios of the ti chip, but i believe my digi-key search linked above was not limited by pin count
so maybe the only reason fram costs more is that ti doesn't license the fram patents to chinese companies? it still beggars belief that ti (and microchip, st, etc.) would be spending three dollars a chip on 8k of nor, or even three dollars a chip divided by two layers of profit margin
AVR64DD14 is $1.20 qty25 for 64kB of Flash and 8kB of SRAM (and quite a bit more analog features, like dual-power supplies, more ACs, DAC, Differential ADC...).
So I'm pretty sure NOR Flash remains quite cheap. TI's MSP430 are all cheapest with FRAM though, so your question is curious. I admit I don't know where to go or how to investigate your question however. I don't really use MSP430 myself, I just know thats what is commonly associated with FRAM in the literature I've read.
The main application here would be that the RP2040 only has a single XIP QSPI bus. If you extend its memory by hooking up PSRAM to that bus, you can't boot because the chip loads all its code from QSPI. If you hook flash up to that bus, you don't have any way to add extra memory.
FRAM would allow you to have your cake and write it: your application code survives a reboot, and (if the chip were to gain write support) the remaining space could be treated like PSRAM.
i see, that makes a certain amount of sense, thank you. normally you can share a single spi or dual/quad spi bus between multiple peripherals with different /cs lines, but i guess that would be pretty tough to make work for instruction fetches. older chips like the 8086 had a pin to tell the memory system when it was fetching an instruction, but i haven't seen that feature in a long time, not even enabled by a fuse
you can probably use qpi that way (with both psram and flash) if you sacrifice xip and settle for loading overlays? you could even store them on qpi nand
