[U-Boot-Users] RFC: U-Boot Environment support in SystemAce Compact FLASH

[Keith J Outwater]

u-boot-users-admin at lists.sourceforge.net wrote on 08/22/2005 04:43:15 PM:

> On 8/22/05, Wolfgang Denk <wd at denx.de> wrote:
> > In message <OF8ADB0661.25EF292C-ON07257065.00568E7A-07257065.
> 00576B05 at mck.us.ray.com> you wrote:
> > >
> > > I have completed the initial port of U-Boot to a custom 
PPC405/VirtexII
> > > Pro FPGA board and I am starting to look at ways to store the U-Boot
> > > environment in the CF card used for FPGA configuration by the Xilinx
> > > SystemAce.
> > 
> > Please re-read the archives why this is not as trivial as it may seem.
> > 
> > > I am leaning toward the approach of adding DOS FAT write support and
> > > adjusting the initial U-Boot environment to provide sufficient stack 
space
> > 
> > This won't help you much. In the first step, you would have to modify
> > the whole CF and DOS FAT code such that it works while  running  from
> > flash.  This is a non-trivial task, and I don't intend to accept such
> > modifications for inclusion in the publich tree.
> > 
> 
> Does a system ace CF card have a partition table?  Maybe you could make 
a
> special partition on the CF for this type of info.  You would need a
> sector read
> routine and code to parse the partition table to index into the
> environment sectors.
> You would probably need some ram available (or at least a bunch of 
registers)
> to pull this off.

RAM is not a problem.  VirtexII FPGA based processor systems have plenty 
of RAM for this type of thing.
I like this idea a lot better than just trying to access raw sectors on 
the CF card.  I'll take a look at that.

> 
> Another option might be to store the environment stuff as data to be
> loaded into
> an accessible block ram on FPGA power-up.  I haven't looked at how 
system ace
> handles this sort of thing.  Are the block ram contents stored in
> separate files on
> the CF?

Not as a separate file, but (optionally) as part of the FPGA configuration 
bitstream.
The problem with using block RAM for storing the environment is that it is 
volatile.