Clarify sector/page/word

[JuliDi]

Currently only the terms "page" and "word" are used. However, many datasheets etc. seem to use the following terminology:

• Word: Smallest addressable unit for programming operations (8/16/32 bits).
• Page: Buffer unit for optimized programming, typically 256 bytes.
• Sector: Minimum erasable unit, typically 4 KiB.
• Block: Group of sectors that can be erased together, typically 64 KiB.

My understanding is that currently "page" refers to the chunk that can be erased at once (= "sector").
Not sure whether "page" and "word" are really ambiguous between different documents/implementations.

[diondokter]

You're right. However, not all of these concepts are exposed to us.

How much at a time can be written to the flash in one transaction doesn't matter since we're always on top of implementations that abstract that away.

How the erase is executed is also not important since in the embedded-storage traits expose erase as a 'from' and 'to' pair of addesses.

Also, I feel like when people are talking about flash, they tend to say that you 'need to erase a page'. I find people rarely talk about sectors.

Hence why sequential-storage only talks about words and pages.
A word is the smallest unit that can be written.
A page is the smallest unit that can be erased.

I think we should keep this as the definition because I think this causes the least confusion for most people.

[JuliDi]

How much at a time can be written to the flash in one transaction doesn't matter since we're always on top of implementations that abstract that away.

This is true. However, it might matter when we want to leverage certain properties of NOR flash (like writing all zeroes to a byte to mark something as invalid or so). Not really a concern for this particular crate, but it might be helpful if we could mock these properties.

Also, I feel like when people are talking about flash, they tend to say that you 'need to erase a page'. I find people rarely talk about sectors.

Might there be a difference between NAND and NOR flashes? For example, wikipedia says this:

Modern NOR flash memory chips are divided into erase segments (often called blocks or sectors).

I think it doesn't really matter how you name it, but adding a short description what it means could avoid confusion. Maybe just add this:

A word is the smallest unit that can be written.
A page is the smallest unit that can be erased.