Re: [Qemu-devel] [RFC v5 2/5] hw/arm/digic: prepare DIGIC-based boards support

[Peter Maydell]

On 4 December 2013 20:22, Antony Pavlov <address@hidden> wrote:
> Here is my proposition:
>
> 1. qemu board code setup CPU to start from 0xFFFF0000. (0xffff0000 is a ROM 
> address
> on DIGIC chips)

Sort of. What we need is:
 1a. Add a "hivecs" property to the ARM CPU object (which
just sets env->cp15.c1_sys bit 13)

(this is about half a dozen lines of code max)

 1b DIGIC board init code creates the CPU and sets the hivecs property on it

(another handful of lines of code)

> 2. we need somehow put a 'jump-to-beginning-of-ROM' instruction to 0xffff0000.
> (We can't put barebox to 0xffff0000 as barebox image is bigger that 64K.)
>
> There is at least two possibilities to do so:
>  * we can use specially prepared ROM image;
>  * qemu board code can insert by itself a 'jump-to-beginning-of-ROM' 
> instruction
> after loading ROM image (as qemu MIPS Malta board code does).

The board code should definitely not be writing random instructions into
memory. You need to provide a ROM image which will do the work.

> 3. CPU starts as usual. Branching to barebox code in ROM happends in a 
> natural way!

This bit's OK :-)

thanks
-- PMM