Re: [ECOS] PowerPC vector base location

[Gary Thomas <gthomas at redhat dot com>]

On Sun, 2001-12-23 at 02:13, Bob Koninckx wrote:
> Hi guys,
> 
> I'd like to introduce an extra configuration option into the powerPC
> HAL.
> The powerpc architecture allows the vectorbase to be located at
> 0x00000000
> or fff00000. Not every board however has memory at 0xfff00000. Depending
> on
> the platform, 0x00000000 can be RAM or FLASH or ... 
> 
> Therefore I think that it makes sense to rewrite the CDL option for the
> vector
> base as follows.
> 
>     cdl_option CYGHWR_HAL_POWERPC_VECTOR_BASE {
>         display       "Exception vectors location"
>         description   "
>             PowerPC exception vectors can reside either at 0x00000000 or
>             0xfff00000. The startup type and platform HAL controls which
>             is used."
>         flavor        data
>         calculated { (! CYGHWR_HAL_POWERPC_FORCE_VECTOR_BASE_LOW &&
>                        (CYGHWR_HAL_POWERPC_FORCE_VECTOR_BASE_HIGH ||
>                        (CYG_HAL_STARTUP != "RAM" &&
>                         ! CYGSEM_HAL_POWERPC_COPY_VECTORS)))
>                       ? 0xfff00000 : 0x00000000 }
>     }
> 
> If the platform HAL does not define
> CYGHWR_HAL_POWERPC_FORCE_VECTOR_BASE_LOW,
> nothing changes, so there is no risk of breaking existing code. It
> leaves however
> the option to force the vector base at zero with copying (for RAM at
> 0x0000) or 
> WITHOUT copying the vectors. (FLASH 0x0000000)
> 
> This would be good to have for e.g. MPC555. Copying the vectors is than
> usefull for
> platforms that disable the internal flash and dual map it to a RAM
> region. Not copying
> allows for using the Internal flash. (an attempt to write to that one
> will result in 
> an illegal instruction exception)
> 
> Any comments, suggestions ??

This is a fine idea, as long as care is taken to not break anything :-)

Do it, test it, send the patch & the [copyright] assignments and we'll 
integrate it into the source tree.

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