Re: Passing information from bootloader to Zephyr


Marti Bolivar <marti.bolivar@...>
 

Hi,

David's threads didn't get much response, but while looking at some STM32 rework in Zephyr, I thought it was worth another try.

On 28 June 2017 at 13:29, Marti Bolivar <marti.bolivar@...> wrote:


In general I also think that we need to start thinking about other issues related to passing control from mcuboot to Zephyr. Beyond just setting up the stack and jumping to the entry point, mcuboot on Zephyr also locks IRQs and disables the system clock. However, those aren't the only hardware resources it uses, and it isn't always "clean" about putting them back into their reset state.

For example, Zephyr mcuboot currently leaves the STM32 clock tree configured to use the PLL, it leaves devices powered on, clocked, and configured (e.g. UART), etc. The story is similar on other targets.

Leaving this vaguely defined is undesirable, especially for power management.

It's likely future work, but it seems inevitable we'll have to define exactly the state of the device that mcuboot provides to the chainloaded image. Having a place to put formal definitions will simplify this work.

I especially want to highlight this part: ^^

Erwan, I noticed while looking at a recent PR [1] that the STM32 UARTs have a status = "disabled" property in DTS (not introduced in this change, was already there).

But in fact, when Zephyr is chain-loaded by mcuboot, at least one of the UARTs is not disabled, since mcuboot uses it to log and doesn't disable it before jumping to the next image. Further the clocks are reconfigured from their reset defaults, the PLL is on, etc.

It seems like this will inevitably cause problems as the Zephyr DTS continues to get more sophisticated (not just for STM32).

Am I missing something here?

Thanks,
Marti


 

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