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programing an intel cpu

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Gaston

Member
this queston is just for curiuosity sake. i have no intent on trying it. ...yet : )
is it possible to program lets say an intel 486 processor like you do a pic? if so what are the instruction set. is there a list somewhere? and what hardware would you use. boot it off of a floppy and then install your program like loading windows?
 

HarveyH42

Banned
A PC CPU is completely different. A microcontroller has CPU,memory and I/O circuits, plus a bunch of other support stuff. It's almost a complete computer inside a single chip, pretty much everything that can be packed inside.

The CPU in a PC, is just the processor. It does all the math, but by itself, it has no place to fetch numbers or place the results.
 

Gaston

Member
i think i get the idea. the program is read off of the hard disk and placed into ram. the the cpu takes it from there? is there still a way to write an operating system by your self?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Gaston said:
i think i get the idea. the program is read off of the hard disk and placed into ram. the the cpu takes it from there? is there still a way to write an operating system by your self?

Yes, but you're over complicating things, a computer consists of three basic things:

1) A processor
2) Memory
3) I/O

In the case of a PIC (or other micro-controller) all these are included in one tiny chip.

With a 486 you require a LOT of extra circuitry to get it to do anything, in particular you need to supply external memory and I/O facilities.

There's no need for an OS at all, that's only a convenience added to a full computer, there's no need for even a BIOS (as a PC does), this is only a layer of the OS.

You could simply write everything you need from scratch, using hand assembled machine code, and indeed that's how it used to be done. But you soon find out that almost every program you write uses a number fo similar routines - for example to read a key from a keyboard, or to output a byte to an RS232 port, or display a character on a screen. It makes sense to only write these once, and reuse them as required - these essentially become BIOS or OS routines.
 

hjames

New Member
If you dig around for the "LinuxBIOS" project, you can get a rough idea of what happens. Standard development tools can be used for the most part, but you end up needing to strip all the low level software dependencies.

At this level, the easiest thing is to burn an EEPROM/Flash chip and dump it into a socket connected directly to the proessor's data bus, unless you really want to rewrite an IDE/filesystem driver. or a network stack.
 

Sceadwian

Banned
Modern CPU's and motherboards are really too complex to atempt this kind of thing anymore, there's just too much to acount for and work around.
Look around for 'biscuit' PC's or PC modules on google. You can find plenty of very basic X86 archtecture CPU's with support systems that fit into roughly the space of a breadboard. These are much easier to deal with, as the bios is usually simple and straightforward, they also tend to have some CPU accesable digital or analog I/O as well as they're inteded for embedded applications.
 

HarveyH42

Banned
I think this was more of a 'what to do with this ancient CPU' pondering... Kind of like my draw full of RAM chips, SIMMs and DIMMs...
 

Sceadwian

Banned
Geek accesories. Just desolder them. If you don't care if the components actually survive, support the board upside down in an oven and put a catch tray under it. Heat the board and the SMD components wil lat some point just fall off. I don't think this will work very well in an electric oven, but a regular or convection gas oven would work well.
 
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