Messages in this thread | | | From | Paolo Ornati <> | Subject | Re: [OT] Documentation for PC Architecture | Date | Tue, 19 Aug 2003 10:01:42 +0200 |
| |
On Tuesday 19 August 2003 03:02, Jamie Lokier wrote: > > The MMU _is_ used to remap memory addresses. It is part of the CPU itself. > But it translates what's called "virtual address" space to "physical > address space". Physical addresses seemingly map directly to RAM and > memory-mapped I/O.
I know...
> > Paolo's question is, what happens to the 384k of _physical_ addresses > starting at 0xa0000, which should correspond with 384k of actual > physical RAM?
It seems that only you have understand my question! :-)
> > If you use the MMU to map a virtual address to the physical addresses from > 0xa0000..0xfffff, then whichever virtual addresses you chose will map to > video memory, ROM, BIOS etc. > > The answer is that after the MMU has translated, a _second_ address > translation takes place, outside the CPU, which maps the physical addresses > so that a hole is created in the RAM without any RAM going missing. This > second translation is done by the motherboard chipset.
OK.
> > Enjyo, > -- Jamie
VERY [OT]:
Why do I do all these questions? At present I'm working on a very small kernel (PabloX :): - it's very simple: it only uses segmentation and has drivers only for stupid things like AT-PS/2 keyboard (do you have USB keyboard? I'm sorry!) - some (a lot of) code is taken from linux 0.01 / 1.0 / ...
If anyone want to see this stupid thing: http://members.xoom.virgilio.it/javaman/
NOTE: don't read the comments in source code! They are a mix of pseudo-English and Italian!
To try it: tar xzf pablox.tar.gx cd pablox/ make
now you should have a floppy image in ./IMAGE, I suggest insert a floppy and do "make disk", than reboot and see keyboard leds! (if you have an AT or PS/2 keyboard)
press (1,2,3,4) to switch to console (1,2,3,4): the consoles are stupid! All the programs write to the current console... press "ESC" to reboot!
Bye, Paolo
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |