Re: [MiNT] Memory protection

[Michael Schwingen <rincewind@discworld.dascon.de>]

On Fri, Feb 19, 1999 at 02:16:58AM +0100, Henk Robbers wrote:
> 
> This is very interesting to know. What you say is that parts of the
> logical address spaces are going to digress from the physical space, and
> that de facto you have implemented what I think is unavoidable for a full
> paging model in MiNT. But I think you use it in such a way that the effect
> is a mere amalgamating of ST and TT ram. The displacement from physical
> space is a constant for all TT ram pages. Am I right?

No. We still have ST- and TT-RAM (ISA DMA is only possible in the lower
16MB, which is identical with ST RAM).

The Offset in TT RAM is not constant - you can reduce the amount of ST RAM
to 4 or 8MB, which means that the rest is moved up to TT-RAM, and each
of the 8 memory banks start at a multiple of 64MB in address space, which
means that you get holes in the physical address space unless you put 512MB
into the machine.

The PMMU is set up so that you have one contiguous block of TT RAM (in
virtual address space).

This also means that drivers which do DMA in TT RAM (like my SCSI driver)
must support scatter/gather DMA, since one transfer may span multiple
physical blocks.

cu
Michael
-- 
Michael Schwingen, Ahornstrasse 36, 52074 Aachen