Re: [Modularkernel-developer] PhysicalKernelStart, PhysicalManagedStart

[Tomas K. <tom...@gm...>]

On Fri, Apr 9, 2010 at 11:24 PM, Daniel Oertwig
<mus...@go...> wrote:
> Am 09.04.2010 23:17, schrieb Tomas Klacko:
>> Hi,
>>
>> in physical_memory.c, are PhysicalKernelStart and PhysicalManagedStart
>> always going to have the same value? (0x100000)
>>
> They can, as it is at the moment, but it is not necessary.
> The two variables describe two completely different things.
> The one is the start of the kernel, which is somehow a constant thing,
> because loading to 1 MB mark is the "standard" for kernels.
>
> The PhysicalManagedStart is the value describing at which point in
> memory we start tracing whether it is used or not. So at the moment, we
> cannot say whether memory before 1 MB is used or not.
>
> I am thinking to change that, because it is somehow nonsense to not
> manage a part of the physical memory.

Well, only unless you do not want to manage some part of the physical memory,
which I get is the nonsense :)

> Its a relict from previous code, where I thought (which was wrong, as I
> know now) that PHYSICAL memory under 1 MB is needed for DMA, but in fact
> it is VIRTUAL, so there should be no problem managing all physical
> memory in the same way :)

Interesting, what is your previous code about?

Where did you get this information that memory under 1 MB is not needed for DMA?
I recall that like the first 16 MB is used for DMA, because some devices
simply cannot address higher memory for their DMA transfers.
Does it have to do with IO Ports (and a lot of RAM, like plus 4GB)?

Tomas