Hello Radek Hnilica,
(if you'd said were you're from I would have attempted to say hi in your
native language..)
You have some interesting ideas, I would like to comment on a few please see
below...
Simon Wood
Hardware Engineer
Pace Micro Technology plc
Victoria Road, Saltaire, Shipley
West Yorkshire, BD18 3LF
Tel : +44(0)1274 532000 Fax: +44(0)1274 532029
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> -----Original Message-----
> From: Radek Hnilica [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, July 07, 1999 8:55 AM
> To: [EMAIL PROTECTED]
> Subject: Hardware
>
> I was thinking much about it, ELKS, and small embeded
> computers. As I know, there is no suitable hardware. You can
> say that there is a pile of old PC's (are not small), someone in
> this list was talking about embeded controller based on 80186
> and someone else about Z80 processor which is not supported now
> (all these have lack of some sort of memory protection). If you
> know anything else I don't, let me know about it.
[<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embedded OS, there are huge numbers of out of date machine being buried as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.
> Imagine how you protect your system before crackers, and of
> course before yourself. The cracker problem you can resolve
> with some pain. Do not connect your small system to network of
> any type and physically protect it before unauthorized access.
> But you can not protect it before yourself. One badly written
> command in your program can cause a kernel goes to heaven or
> hell (you can choose). See I do not write one malicious command
> but one baddly written command (I have a typo on my mind).
[<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.
> 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.
> 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.
> 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)
