Comments on Retro Programming: Itsy-OS Kernel: Preemptive Switcher & Memory Manag...

I have just found your blog suddenly. It is full o...

2011-04-12T14:26:06.703-07:00

I have just found your blog suddenly. It is full of very interesting informations i thinked on before.

Once i was got some little time, and i was thinked it would be cool to know more from the x86 architecture. So i just goed to play a bit in C, i downloaded from somewhere an ebbeddable X86 binary disassembler and readed 8088 and 8086 specifications, and i have put together an x86 emulator. I first emulated the CPU, i have reverse engineered the instructions up to 80286. Then i putted together a very simply BIOS emulation, then a graphics card emulation to see some picture (with support of text mode and 320x240 via bios call), and keyboard emulation. With a very little interrupt support. Coding these things was taken a total 3 day from my life, and at the end of the project i was able to run some simply dos .com files, wich painted animated smyleis and dogs out on the picture.

The the project was succesfull. After i was done with it, i started to hate x86 much more than i have haten an architecture ever. Probably i would not even touch x86 assembly, or the x86 architecture ever. I have never seen so badly designed architecture before. X86 is simply one of the worst architecture ever created.

But some times, these things are coming into my mind again and again, maybee becouse there is still a lot of interesting things, that i must check.

Great stuff but now I really want an implementatio...

2011-04-05T13:02:12.382-07:00

Great stuff but now I really want an implementation that will run on my abacus. :-)

Have only just found your blog. Fabulous!

interesting. i started working on similar kernel l...

2011-04-01T10:25:21.265-07:00

interesting. i started working on similar kernel last year. screenshot of what i've got:

http://rubbermallet.org/retros-partitions.png

it uses the same sort of techniques you are using. i'll post the source for my task switcher tonight. i'm at work and it's at home on my laptop.

In task switcher (E_SWITCHER), [quote] ; save the...

2011-04-01T09:07:22.098-07:00

In task switcher (E_SWITCHER),

[quote]
; save the registers of the current process
push ax
push dx
push bx
push bp
push si
push di
push es
push ds

; save the stack of the current process
mov di,M_STKP
cs mov ds,word[di+D_PCP-M_STKP]
mov word[di],sp ; M_STKP
[/quote]

the last mov sp will not reflect correct Stack pointer for the process, as 8+ items of data are pushed to current stack.

May be I'm wrong, please correct me.

This is extremely cool. One of the reasons I thin...

2011-03-31T05:26:45.137-07:00

This is extremely cool. One of the reasons I think DOS was cool is that it could be so easy to understand. A bit like Menuet and Kolibri.

Beautiful...

2011-03-30T21:55:37.696-07:00

Beautiful...

@Anonymous: IIRC the original 8086/88 didn't ...

2011-03-30T18:43:15.747-07:00

@Anonymous:

IIRC the original 8086/88 didn't have pusha/popa.

anonymous: Itsy is strictly 8086 code. pusha/popa...

2011-03-30T18:39:24.450-07:00

anonymous: Itsy is strictly 8086 code. pusha/popa require at least an 80186 :-)

Just a thought after a quick pass through of task ...

2011-03-30T17:52:51.843-07:00

Just a thought after a quick pass through of task switcher, but wouldn't it be simpler to use a call to pusha/popa to push/pop all of the registers on/off the stack. Not sure if you've already though of that or if you're using a more limited subset of registers, but every bit helps =)

If you plan to port this to other architectures, y...

2011-03-30T16:13:59.566-07:00

If you plan to port this to other architectures, you may want to have a look at Mike Pall's DynASM. Mike is the author of LuaJIT, he uses DynASM to generate the ASM code of the LuaJIT interpreter for several architectures (x86, x64, MIPS and soon ARM) from the same a common code base, augmented with platform specific extensions.

http://luajit.org/dynasm.html

Neat. I'm working on a very limited machine ca...

2011-03-30T15:50:08.168-07:00

Neat. I'm working on a very limited machine called the Hydra (32K shared ram, 128 K SRAM) and will indeed use this as food for thought

cool

2011-03-30T15:41:46.461-07:00

cool