Hello Simon
> (if you'd said were you're from I would have attempted to say hi in your
> native language..)
My native language is Czech.
> You have some interesting ideas, I would like to comment on a few please
> see below...
> [<Simon Wood>]
> To my understanding ELKS is aimed as a teaching project as well as an
> embedded OS, there are huge numbers of out of date machine being buried as
> trash, hopeful ELKS will bring new life to these machines. Some machine
> based around the 8086 do have memory protection (the Psion Series 3 for
> example), where this is available I expect it will be used BUT it is not a
> requirement for ELKS.
What a memory protection if a processor itsef doesn't have protected
mode. You can design what you can to death, but program runing in
user space may do what ever it want.
> [<Simon Wood>]
> You are correct that a bad or malicious command could crash the kernel,
> but remember that a cracker would have to get code onto the machine in the
> first place. With well written code this shouldn't be a problem.
No code is perfect except .....(complete name). Hardware with memory
protection is much secure than without it.
> > I thing that there are two ways to resolve this problem.
> >
> > First way is hardware way. A construction of cheap
> > hardware with protected mode and memory protection scheme is
> > needed. This one is big problem, how many 16-bit processors
> > with protected mode, and memory protection you can use. I know
> > about I80286, J-11 (LSI-11, DCJ-11, K1801VM1), if you know more,
> > let me know. Are these processor yet on market? I think no.
> > But we can design our own processor, and model it in FPGA
> > (Xilinx or other). This needs much work and advanced experience
> > in hardware projecting and construction.
> [<Simon Wood>]
> Possible but seems like an awful lot of work for a 'free' project.
Yes it's lot of work. But if target is more interesant, more peoples
will help.
> > Second way is software way, its way of emulators. You can
> > emulate some hardware architecture which meet your needs. Bad
> > news is that this cost much in speed. Slowdown need not be to
> > big, not as you expect. And well designed hardware may have
> > some advantages in memory savings You can code a often used
> > sequences to one simple instruction and save much space in code
> > segment.
> > If you begin with software emulator you may in future build
> > an hardware which use same instruction set and thus save all
> > previously done work.
> [<Simon Wood>]
> Software Emulators can fill the gap before hardware is available, but they
> often don't behave exactly as the real thing. If you have a particular
> hardware target in mind then they are a useful tool.
I' was thinking about PDP-11. It's 16-bit architecture, has memory
protection, it's nice architecture. Some software emulator exists.
First I was thinking of separate MMU. Such a MMU can be done maybe
in one Xilinx chip, and can be connected to any processor with 16 bit
address bus. A management of this MMU is done through a memory
addresses in upper 8kB (4kW) of address range. This is very nice.
But problem is a processor which don't have protected mode, and a
signal pin which can tell MMU what is going on.
Before we begin model a processor in FPGA we can model it in
microcontroller such as ATMEL 89C51 or some from MICROCHIP PIC. Make
design as clean as possible.
Step one: Microcontroller(CPU,MMU), memory, pheripherals.
Step two: Microcontroller(CPU), FPGA(MMU), memory, peripherals.
Set three: FPGA(CPU,MMU), memory, peripherals.
Last step: FPGA(CPU,MMU), memory, FPGA(peripherals).
> > Are you asking why am I writting this? A month ago I found
> > an emulator of PDP-11 minicomputers family. I also found a
> > couple of software for it including old unix V5, V6, V7. And
> > for some bucks you can get an License for ancient unix source
> > code. And get a BSD2.11 unix with source code to. Then I begun
> > thinking about hardware emulator and also porting ELKS to this
> > hardware.
> [<Simon Wood>]
> we look forward to a /arch/pdp-11 tree appearing soon ;o)
Will be nice, can try it under some emulator.
As I say in previous message, I have not experience in FPGA design. I
look around and found VHDL language and some tutorial, but still
don't know how what is needed to program an FPGA for instance from
Xilinx.
PS: Target will be small embeded computer size of about A6 x 3 cm.
Which run under UNIX like OS.
Radek Hnilica
E-mail: [EMAIL PROTECTED]
http://www.linuxfan.com/~radek_hnilica
