Re: [Qemu-devel] armv7m/stm32f205 not starting if code linked from 0x08000000

[Liviu Ionescu]

> On 08 Jun 2015, at 20:43, Peter Maydell <address@hidden> wrote:
> 
> ... Unfortunately the test we're doing to decide is calling rom_ptr(),
> which only looks at the addresses the ROMs are registered to
> be copied into; it doesn't know about aliasing.

I guessed so.

> If you fudge the if() statement to use 0x08000000 rather
> than 0 as the address passed to rom_ptr() it will probably
> work.

I tried the following:

        rom = 0x08000000; //rom_ptr(0);
        if (rom) {
            /* Address zero is covered by ROM which hasn't yet been
             * copied into physical memory.
             */
            initial_msp = ldl_p(rom);
            initial_pc = ldl_p(rom + 4);

unfortunately it crashes with a segmentation fault a bit later.

> I'm not sure what the correct fix for this is, though.

the actual configuration is:

- a flash region is created at 0
- an alias region is create somewhere else (at 0x08000000 for stm32, different 
for other vendors)
- the application image can be linked either at 0, or at the aliased address, 
and there is no way to enforce one of them
- the application image is loaded by the famous ELF loader either at 0 or at 
the aliased address, both cases are equally possible, and as such both must be 
supported
- the reset code tries to fetch the two pointers (msp & pc) from 0 and 4, but 
the content might not be at zero, but in the aliased region, and both cases 
must be supported.

> ... two-phase reset ... the CPU *comes out* of reset,
> ... the reset function is the best we
> can do, and you end up with this ugly hack.

yes, I guess I understand what you mean, but in this case I don't think the 
problem is that theoretical, it is just an implementation issue, the original 
arm reset code was not written with aliased regions in mind.

I don't say it is simple, because I don't know enough details on how memory 
regions and aliases are implemented, but I guess that someone that has more 
qemu experience than I do can find a nice solution.


regards,

Liviu