Who initialize the flash? [closed]

StackOverflow https://stackoverflow.com/questions/22229590

Question

I am learning about Linux boot process on ARM processors and find that U-boot is boot from the flash and then u-boot code intialize the RAM to set up the execution environment like stack set up and all and relocate itself.

Now my question who initialize the flash so that u-boot code can execute?

Also is it any difference booting it from NOR flash or NAND flash?

Is booting from NOR flash is faster than booting from NAND flash?

Was it helpful?

Solution

naturally someone has to program that flash the first time. And each board design determines how that actually happens, sometimes the part is programmed before being soldered down, sometimes there is a backdoor a connector you can program through, etc. Sometimes not. Sometimes the processor or other hardware on the board has some other kind of bootloader that you can use to program that normal boot flash, etc.

NOR or NAND isnt usually much of a difference, my biggest problem with the newer flashes is worrying about read-disturb. Flash reading is faster than writing and a lot of the effort is or at least needs to be in write speed and density and cost, so I would assume that is where the efforts are and not so much read speed vs write speed. If you have a read speed problem, then just copy the bootloader to ram as soon as you can and run from there, stay off the prom after that.

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