Re: [ECOS] Regarding to eCos on VRC4373

[Nick Garnett <nickg@cygnus.co.uk>]

"Ling Su" <lingsu@palmmicro.com> writes:

> > > <2>. We have some communication application developed on the board,
> > > unfortunately the eCos defaultly in Big Endian mode for VRC4373. Since
> > > communication application usually in Little Endian mode, I don't know
> the
> > > rational reason behind the Big Endian choice for this platform, and I
> also
> > > would like to know the possibility to compile eCos GDB stub and lib in
> > > Little Endian mode, can we do it smoothly or need any hacking on the
> source
> > > code?
> >
> > You will probably need to make some adjustments in the platform code. But
> > I believe the architecture and variant HALs should work because we have a
> > v4300-based internal board that used to be little-endian if I remember
> > right.
> >
> 
> Can you disclouse which vr4300 based board is running eCos, I am just
> curious since I didn't find any supported platform on eCos website except
> the vrc4373 evaluation board.

We originally did the port to the VRC4373 in little-endian mode
because, as you point out below, PMON runs in little-endian
mode. However, the customer we were doing this for wanted to run in
big-endian mode, so we swapped it over.

Other boards, such as the TX39 run in little-endian mode, so the HAL
architecture code should be OK. Only the platform code may need some
work.

> 
> I briefly checked the platform code, I didn't find any specific point to
> modify since the Macro define CYG_LSBFIRST or CYG_MSBFIRST looks to me take
> care of a lot of endian issues. I am just wondering why the Little Endian
> mode is illegal for VR4300 platform. What I can think of doing first is to
> try to enable it and make the monitor, is that doable?
>

The main thing that might cause a problem is access to the
devices. While some of the chips will swap endianness with the CPU,
others may need some changes to the access software to cope. I don't
recall the exact details.


> Since I found the PMON comes together with NEC board is Little endian, can I
> just complile the eCos lib in Little endian mode and debug it using PMON?
> Any comments on this way? Thanks a lot!
> 

That is certainly worth trying. However the PMON code in the HAL has
not been used for some time, so it may be out of step with the rest of
the system.

-- 
Nick Garnett, eCos Kernel Architect
Red Hat, Cambridge, UK