[ECOS] ecos start in ram

[ECOS] ecos start in ram

[james chen]

 Hello,

        now I am porting eCos to my test board (based ARM7TDMI), the ROM
address is 0x0 and the
 RAM address is 0xc000000, but in ecos the RAM address is 0x0, so how to
config memory layout to run Redboot and eCos? I also think the vectors.S
file should be changed, will you tell any?

  Thanks

  james chen

RE: [ECOS] ecos start in ram

[Gary Thomas]

On 16-Feb-2001 james chen wrote:
>  Hello,
> 
>         now I am porting eCos to my test board (based ARM7TDMI), the ROM
> address is 0x0 and the
>  RAM address is 0xc000000, but in ecos the RAM address is 0x0, so how to
> config memory layout to run Redboot and eCos? I also think the vectors.S
> file should be changed, will you tell any?

This sounds very much like the Assabet (SA1110) system.  We use the MMU
to remap memory, swapping the RAM and ROM addresses around.

Re: [ECOS] ecos start in ram

[james chen]

my test board have no MMU, will you give suggestions?

>
> On 16-Feb-2001 james chen wrote:
> >  Hello,
> >
> >         now I am porting eCos to my test board (based ARM7TDMI), the ROM
> > address is 0x0 and the
> >  RAM address is 0xc000000, but in ecos the RAM address is 0x0, so how to
> > config memory layout to run Redboot and eCos? I also think the vectors.S
> > file should be changed, will you tell any?
>
> This sounds very much like the Assabet (SA1110) system.  We use the MMU
> to remap memory, swapping the RAM and ROM addresses around.
>
>

Re: [ECOS] ecos start in ram

[Bart Veer]

>>>>> "James" == james chen <james_ch1@sina.com> writes:

    James>         now I am porting eCos to my test board (based
    James> ARM7TDMI), the ROM address is 0x0 and the RAM address is
    James> 0xc000000, but in ecos the RAM address is 0x0, so how to
    James> config memory layout to run Redboot and eCos? I also think
    James> the vectors.S file should be changed, will you tell any?

IIRC on some ARM processors you normally need RAM at location 0x0,
because that is where interrupt vectors etc. are held. You also need
ROM at location 0x0 because bootstraps happen from that address. In
the absence of an MMU, the normal way to resolve this is to have a
memory remap facility: on power up there is ROM at location 0x0, so
bootstrap can proceed; early on during the bootstrap, the remap switch
is toggled and the memory map changes; the ROM moves somewhere else in
memory, and there is now RAM at location 0x0 so that the interrupt
vectors etc. can be updated.

So for a typical eCos application, the RAM might be at 0xC0000000
immediately after power-up but it will be remapped to 0x0 early on.
Hence the eCos memory map will have RAM at 0x0.

The exact details are of course hardware-specific, and will have to be
addressed by your platform port.

Bart

Re: [ECOS] ecos start in ram

[Grant Edwards]

On Fri, Feb 16, 2001 at 02:32:23PM +0000, Bart Veer wrote:
> 
>     James>         now I am porting eCos to my test board (based
>     James> ARM7TDMI), the ROM address is 0x0 and the RAM address is
>     James> 0xc000000, but in ecos the RAM address is 0x0, so how to
>     James> config memory layout to run Redboot and eCos? I also think
>     James> the vectors.S file should be changed, will you tell any?

For a while I ran eCos with ROM at 0x0.  It's a pain.  You'll
have to modify vectors.S to move the "fixed vectors" stuff
somewhere else (the vsr_table is the part that seemed to
matter).  Then you'll have to modify the routines that write to
the vsr_table -- last time I looked, some of them assumed it
was at a particular hard-wired address.

You'll also have to set up your ROM so that the interrupt
vectors (except for reset) point to code that does indirect
jumps via a jump table in RAM.  NB: This table is different
than the vsr_table in the fixed vectors sections.  Then you
need to modify the startup code in vectors.S so that it fills
in this table instead of of locations at 0x00-0x20.

The really painful part is that you have modified
"architecture" HAL files that aren't part of your platform HAL.
Updating to newer versions of eCos requires re-doing the same
changes again to the architecture HAL files.

> IIRC on some ARM processors you normally need RAM at location
> 0x0, because that is where interrupt vectors etc. are held. You
> also need ROM at location 0x0 because bootstraps happen from
> that address. In the absence of an MMU, the normal way to
> resolve this is to have a memory remap facility: on power up
> there is ROM at location 0x0, so bootstrap can proceed; early
> on during the bootstrap, the remap switch is toggled and the
> memory map changes; the ROM moves somewhere else in memory, and
> there is now RAM at location 0x0 so that the interrupt vectors
> etc. can be updated.

Re-mapping is _far_ easier than what I previously described.
You can still run with your code in ROM if you want to, but
it's easier debugging if code is in RAM.

> So for a typical eCos application, the RAM might be at
> 0xC0000000 immediately after power-up but it will be remapped
> to 0x0 early on. Hence the eCos memory map will have RAM at
> 0x0.
> 
> The exact details are of course hardware-specific, and will
> have to be addressed by your platform port.

If you don't have a way to remap memory, make the hardware guys
add a way.  It only takes a few gates and a flip-flop.  They've
probably got more than enough extra capacity in that PLD.

-- 
Grant Edwards
grante@visi.com