Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU at 528 MHz

Re:Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU ... by dmitrygr on Thursday June 18, 2020 @02:37AM (#23560396)

> Start with MMC clock frequency at 52 MHz instaed of 400 kHz.

Whoa there!

Spec violation. Not guaranteed to work. Might work some days but not others.

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Re:Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU ... by eerimoq on Thursday June 18, 2020 @02:45AM (#23560427)

The goal is to not configure the MMC at all in Linux, but just rely on the bootloader has already configured it.

Btw, where can I find the spec? And where in the spec can I read about this? Is this true even if we know the MMC supports 52 MHz?

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Re:Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU ... by OnACoffeeBreak on Thursday June 18, 2020 @07:53AM (#23562188)

https://www.jedec.org/sites/default/files/docs/JESD84-B451.p...

You can use http://bugmenot.com/view/jedec.org to get free-to-use credentials.

The section in point is "A.6.1Bus initialization".

I'd say that if your MMC works fine going full-speed out of the gate and the IC on the board supports this speed, then you unlikely to encounter any issues.

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Re:Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU ... by eerimoq on Thursday June 18, 2020 @08:15AM (#23562329)

Thank you very much. Very helpful answer. I'll continue to use 52 MHz until I encounter problems (if any).

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Re:Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU ... by dmitrygr on Thursday June 18, 2020 @02:51AM (#23560465)

Spec says initialization shall be done at 400KHz or less. You can Google for sd spec

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Re:Booting embedded Linux in 0.37 seconds on an ARMv7-A CPU ... by eerimoq on Thursday June 18, 2020 @03:00AM (#23560516)

Will fix it at some point =)

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