Linux explorations: flash memory (2)

Continuing yesterday's work on learning about flash memories and
how they work in Linux.

1. More wikipedia
2. MTD documentation

== 1. More wikipedia

https://en.wikipedia.org/wiki/Flash_memory
Lots of informtation, of which I'm summing up what I found most
significative:

* EEPROM:
The whole device needs to be erased before rerites

* NOR:
Random access reads, random access writes on erased words,
block erase.
Erase block size: 64/128/256 KiB.
Suitable for configuration data and firmware.
Suitable for XIP - Execute In Place, firmware directly executed
from flash.
More reliable than NAND (less likely to have bit flips).
Mnemonic: NOeRror :)

* NAND:
Block devices.
Blocks are composed of Pages.
The typical page size is 512/2048/4096 B.
Reads and writes are per-page, erasures are per block.
Less expensive than NOR.
More likely to have errors (each page has its ECC - Error
Correcting Codes).
Faster erase.
Best suited for large size -> common for storage, e.g. USB
drives, [e]MMC...

* Common:
Reset of a block turns every bit into 1.
Programming turns selected bits into 0.
It is feasible (not necessarily implemented) to update words as
long as done by turning further 1 bits into 0.

* Serial Flash (e.g. via SPI bus):
Common as it makes the PCB design simpler.
A RAM buffer might be placed between the SPI bus and the flash,
to increase the speed of data modifications.
A RAM buffer might be placed between the SPI bus and the CPU,
to improve speed (code shadowing).

== 2. MTD documentation

http://www.linux-mtd.infradead.org/doc/general.html

I found this one interesting:
http://www.linux-mtd.infradead.org/doc/nand.html

You are viewing proxied material from dacav.org. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.