Richard:
These seems to be a problem more because of hardware than software. How do
you keep the PC memory from responding to an address that the Deltatau card
is using? When a particular memory is addressed, within the Deltatau's
address space, both PC RAM and the Deltatau will respond, creating a
collision. I don't know of a way using system software (even in the BIOS)
of blocking off areas of RAM (above 1M anyway).
But it is true that low memory (under 1M and above 640K) could be blocked
off in the BIOS so that dual port boards could be used, once upon a time.
We did this on a product we made, but it was very non-portable, and later
model BIOS's did not allow it. To keep our product going, we had to buy
late model motherboards and reprogram the BIOS with older versions, so that
the memory hole was preserved. It was a big problem.
If you find a solution, I would like to know about it. But I believe the
problem is more hardware than software.
/sg
Richard Teltz wrote:
> I have a PC device that has a Dual ported memory interface with an
> addressing limit of 24 bits (a Deltatau PMAC motion control card).
> I need to memory map this into the kernel space for my RTL processes.
>
> My problem is that I can't figure out how to get RTLinux to leave
> me a free page so I can map this device within this 24bit (16Mb)
> limit. My computer has 32Mb of physical memory.
>
> Effectively, I need RTL to ignore a page in the middle of its physical
> memory. The instructions posted for shared memory communications in
> RTL do not help because they are based on freeing space by limiting the
> total memory used by the OS (and hence the free page is at the top
> of the physical memory). In my case, the device's 24bit limit will
> force me to kill half of my available memory.
>
> It has been suggested that I try to hide my device somewhere in low
> memory where PC bios's have traditionally kept space for currently
> out of date devices. This seems a precarious, and certainly not
> portable solution. Am I mistaken?
>
> Any help would be appreciated, even if someone has tried this and
> can confirm that it is not do-able without losing my memory past 16Mb.
>
> thanks in advance
> Rich
>
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