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U-Boot loading kernel from mmc question

U-Boot quantumlight 2 participants 2 messages Feb 19, 2016

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I am trying to figure out how the bootm command in U-Boot works. It seems to be a state machine that goes from start->findos->findother (fdt)->loados etc.

However I am having trouble understanding how, since my linux image is stored in some partition on the device (eMMC), does that get loaded into memory?

Originally I thought this was what bootm_find_os and bootm_load_os does, but they don't seem to access the block devices or filesystem or contain code that reads in the linux and fdt images into memory.

Am I missing a step here?

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#1 lore raw

Dear quantumlight,

Quoted 7 lines · In message <[email protected]> you wrote:

I am trying to figure out how the bootm command in U-Boot works. It seems to be a state machine that goes from start->findos->findother (fdt)->loados etc.

However I am having trouble understanding how, since my linux image is stored in some partition on the device (eMMC), does that get loaded into memory?

No, it doesn't. The 'm' inte "bootm" command name stands for "memory", i. e. "boot from memory". Bootm is used on images that can be found somewhere in the processor's memor address space. So unless you have parallel NOR flash or similar, booting is always a two step
procedure: in the first step you load the image from MMC into RAM, then you use bootm.

Best regards,

Wolfgang Denk

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