Re: non volatile ram disk

[Peter Wächtler]

Erez Doron schrieb:
> 
> the exact log i get:
> 
> Creating 3 MTD partitions on "SA1100 flash":
> 0x00000000-0x00040000 : "bootldr"
> mtd: Giving out device 0 to bootldr
> 0x00040000-0x02000000 : "root"
> mtd: Giving out device 1 to root
> 0xc2000000-0xc4000000 : "rd"
> mtd: partition "rd" is out of reach -- disabled
> 
> notes:
> 1. the flash is at physical adress 0-0x1ffffff (32mb)
> 2. the ram is at physical adress 0xc0000000-0xc3ffffff
> i tried to map an mtd device to the second part of the ram, but got
> "partition is out of reach"
> 
> any idea ?

you are confusing the address space of the kernel (starting with 3GB [0xc0000000])
with the addresses of the RAM (the upper 32MB starts at 0x2000000)

Then there will be some CS (chip selects) to distinguish what "bus address space"
to use. Like CS1 for Flash and CS0 for RAM (don't know details of SA1100/iPAQ)

You have to use the special MTD device that talks to system RAM.
Again, I don't know the details, but menuconfig gives you:

RAM/ROM/Flash chip drivers
	Support for RAM chips in bus mapping

Self-contained MTD device drivers
 	Uncached system RAM (NEW)

The former sounds like RAM on expansion bus, the latter seems to be
what you are looking for.

Now: is the RAM battery backed, or not? If not, you want to use
the flash as nonvolatile disk - otherwise there would be no need 
to restart the system and hence a normal RAM disk would be nonvolatile.

> 
> On Mon, 2002-01-21 at 15:42, Erez Doron wrote:
> > hi
> >
> > thanks for replying,
> >
> > I already tried to map an MTD to physical memory, but got an error and
> > an mtd with size 0
> >
> > dou you know why ?
> >
> > regards
> > erez
> >
> > On Mon, 2002-01-21 at 15:41, Peter Wächtler wrote:
> > > Erez Doron schrieb:
> > > >
> > > > hi
> > > >
> > > > I'm looking for a way to make a ramdisk which is not erased on reboot
> > > > this is for use with ipaq/linux.
> > > >
> > > > i tought of booting with mem=32m and map a block device to the rest of
> > > > the 32M ram i have.
> > > >
> > > > the probelm is that giving mem=32m to the kernel will cause the kernel
> > > > to map only the first 32m of physical memory to virtual one, so using
> > > > __pa(ptr) on the top 32m causes a kernel oops.
> > > >
> > > > any idea ?
> > > >
> > >
> > > a MTD is the way to go, which uses the "reserved" mem area.
> > > I assume that the RAM is battery backed
> > > -