We're still buying the 5V SRAM parallel interface chips. They were supposed to go EOL but are still available. I didn't know about Cypress. And I think Freescale or TI have some other magneto semiconductor technology for NV memory applications, but I don't have any experience with them.
We use 100-400 KHz clock depending on other peripherals. Only change major parameters via user interface or computer comm. link when using I2C non-vol backup. The major use in our products use the bytewide parallel SRAM interface to an intel 80188 style uP. These write through in nS bus cycles. We use CRC or checksums and redundancy to protect against loss of power during updates. Batteries not required. Being the software guy, the FRAM is the best, parallel or I2C. Haven't tried the SPI yet.
Only problem is sole-source by Ramtron in Colorado. Supposed to be licensed by Japanese company too, I think Fujitsu. But have had supply problems, and obsolescence issues too. We use 5v tech in our legacy items, now everything is 3v . Also, we used parallel chips so could use for fast bus access RAM just like normal data memory. Now mostly use I2C serial style for non-vol database for embedded products. The quick write, virtually infinite write longevity can't be beat.
eric: One "trick" is that manufacturers are somewhat "cagey" (non-descriptive) about which sort of Flash you're dealing with, especially when it's a packaged system like a USB stick or an SD (etc.) card.
Eric: Right. We've seen the phenomenon where seldom/never-read pages on our device silently sit there accumulating disturb errors and whe the day comes that we finally read the page, blamm! It's got too many errors to be corrected by the ECC.
It's therefore important that one's Flash File System knows that it has to "scrub" its way through all of the Flash every so often, correcting all the accumulated simgle-bit errors.
Eric: More coverage of write-disturb and especially read-disturb would also be good. Many people don't realize that the data stored in a NAND Flash degrades with *EVERY READ* (albeit at a much slower rate than when neighboring cells are written) so there is can be no such thing as a reliable "Read only" Flash memory; bad block recovery still has to be possible.
Eric: It would be good to add "retention time" to your comparison table. While magnetic disks physically wear out (or develop head stiction, etc.), the data they store lasts until the mechanical device fails. But Flash memories (of all sorts) have their bits decay over time so data stored for (say) 10 years on a device may become unreadable even though the device itself hasn't really "failed".
I work on unmanaged flash devices. I write device drivers for Micron's Flash Data Interface (FDI), which is a file system for flash. This free product is especially useful for Mobile Phones (feature phones, not smart phones).
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Has anyone noticed lately how the chicken at fast food restaurants seems to come from Cornish game hens? And they charge even more for them! As my dad always said, "They sure don't make 'em like they used to."
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