RAM filesystem

We have 2MB of battery backed up RAM, which is not a part of the system RAM.
We want to put a filesystem on this and use it as persistent memory (like
Flash filesystem but on RAM). My options (?):

  1. use devf-ram. In this case we would have to buy the Flash TDK :frowning:

  2. use devb-ram. I’m not sure if this possible. A quick look at the
    documentation didn’t reveal me how to give the address space (i.e. no
    parameters for that).

  3. Use the RAM file-system driver in Robert Krten’s book “The QNX cookbook”.
    Do people use this in real life applications? I suppose I’d have to do at
    least some adaptation here. I already bought the book.

Any other Ideas? In case of battery buffered RAM, should the filesystem be
‘power fail safe’, like flash filesystems normally are?

I would really appreciate any help. Our board is an embedded SBC with
renesas sh7760 processor and we are using QNX 6.3 with SP1.

Regards,
Martin

Martin Nylund wrote:

  1. use devb-ram. I’m not sure if this possible. A quick look at the
    documentation didn’t reveal me how to give the address space (i.e. no
    parameters for that).

There is a (undocumented) “ram address=” option; you give a physical address
which the driver will mmap_device_memory(). Presumably you’d have to modify
your startup or similar to inform the system of the existence of this
memory but make it unusable for normal kernel allocations.

“John Garvey” <jgarvey@qnx.com> schrieb im Newsbeitrag
news:daeejg$buu$1@inn.qnx.com

Martin Nylund wrote:
2. use devb-ram. I’m not sure if this possible. A quick look at the
documentation didn’t reveal me how to give the address space (i.e. no
parameters for that).

There is a (undocumented) “ram address=” option; you give a physical
address
which the driver will mmap_device_memory(). Presumably you’d have to
modify
your startup or similar to inform the system of the existence of this
memory but make it unusable for normal kernel allocations.

Thanks John, That solves the issue with devb-ram. I wonder why the parameter
is undocumented…