Re: [ECOS] small custom bootloader to start an app stored in flash

[Oleg Uzenkov <o.uzenkov@unicore.co.ua>]

Thanks,

I will give it a try with ROM builds.
> On Fri, 24 Oct 2014, Oleg Uzenkov wrote:
>
>> Redboot is a great piece of software. It is just I found that when you
>> enable some important features like FIS support, Redboot reserves
>> extra space in RAM memory.
>> The size of this reserved extra space in RAM equals to the size of the
>> largest section size in Flash. In case of stm32f407 it is 128KB.
>> Internal RAM is 128KB. As John Dallaway pointed out there is very
>> little sense in using Redboot without enough of external RAM on
>> stm32f4 devices. For example for Kinetis it is a different story, the
>> flash sections are uniform and quite small.
>>
>> For small systems external RAM chip significantly adds up to the cost
>> of a device.
>   
> I understand John's point and agree with him. But, he told about using
> debug infrastructure of RedBoot (debugging eCos applications in RAM).
> But, RedBoot is *debug* and *bootstrap* environment for eCos. I pointed
> on another side of RedBoot, *bootstrap*. You can quite run eCos [ROM]
> builds from FIS.

FIS support requires 128KB of ram on stm32.

> Those [ROM] applications may utilize all RAM (128K +
> 64K) on your target. On start ROM application just does overlay RedBoot
> memory.  You saw that yesterday with Rainer's approach (exec). If you
> cannot manage run [ROM] applications with RedBoot command 'go', just
> implement one new command for RedBoot, e.g. 'xip' (as RedBoot already
> uses 'exec' name to run Linux kernel).

As far as I understand, 'go' command should work in theory as it sets 
program counter (pc) to the address of Entry point (not sure about stack 
pointer).

To make a jump  we need to set stack pointer and program counter. And 
this can be implemented inside a new 'xip' command.

> RedBoot will let you to use
> FLASH I/O, load any images, use start scripts, etc., etc. Of course it
> is my opinion only.
>
> Sergei


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