hello,

the subject says very much, now the rest: i would like to write an OS only in RM. therefore i'd like to use EMS for the multitasking, for every task to get a bank. i searched the i-net, but there were only bad informations. almost with int 0x67, which seems to be from DOS. so now i'm searching tuts and information about EMS without DOS-INTS. i hope you can help me,

mfg

JN!

Try here: http://www.rdos.net/
a dos clone with asm code.

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ASHLEY4.

Batteries not included, Some assembly required.

EMS is not a bios service , you have to implement it in your OS
I recommend that you use unreal mode (like fasm for dos)
put your code and stack in conventional memory and data anywhere.
i think that EMS uses virtual mode and paging that is more dificult to implement.

well, i had a look at the code, but i didn't understand it right. i don't understand what "unreal mode" is. the int 0x67 isn't from bios. the main problem is, that i don't know, how to access the rest of the memory. the switches are not so bad, but to access the memory. i hope anyone can tell me how to do it. i found only tuts telling me how to use EMS with DOS, but now tuts telling how to implement it. i hope you can help!

thanks!

There is no way to do that using BIOS.
On older computers that used 8086 and 80286 CPU the EMS was a hardware device : an additional board for Lotus123 Application or some hardware for the 80286 motherboard. Thus such information is old and specific to old hardware, i doubt you will have an 8086 or 80286 mother board to test it.

Once the 80386 CPU come along the EMS and XMS was simulated by the himem.sys and emm386.exe drivers. basically thos drivers whent into protected mode and by doing such had access to the whole memory range and copied the needed "page frame" from that memory to a location below 1M or at 1M+64k (the so caled HMA) so that Real Mode applications where afterwards capable to use the memory chunk.

SO you see the EMX and XMS are of NO use IF you do not want to go into protected mode (at least briefly)... make a memory copy ... and then return to Real Mode.

A "real" real mode OS has to use only 1M or RAM or actually 640K of RAM since the 640+ area is reserved for additional boards/hardware.

There could be some use IF you have an old 8086 + EMS additional board or an 80286 motherboard that has EMS hardware on it... but the chances are very small...

"Unreal Mode" is a mtehod of using the whole memory in real mode after a brief switch into protected mode and a return... with changed selectors limits...

Is using an bug in 80386 and upwards CPUs that will retain the wrong limits when returning from protected mode...and by doing so you are "somehow" allowed access to a wider range of RAM from real mode...

but it is not a "real" real mode --> so the name is "UNReal Mode"

thank you for all the information! that's a good idea to go into PM and do it there. but how many time needs it to switch to PM and back? does anyone know? thank you. i always thougt, that the ram gets deleted by switching.

You will only need to do the switch once, to set up selectors. After that you switch back to (un)real-mode and have access to all memory and still be able to use BIOS...

You can problably find info on google or osdever.net on how to do the switch.

@bubach: why have i access to all memory? in RM the registers are still 16 bit large, so why have i access to the rest without shiftig all the time? i don't understand! i've already some tuts for PM.

well, ok. i've the code to setup the PM. i would load the deskriptor behind the RM-Memory-Area at 0x10000 linear. but because of the A20 Gate i'll have to load it to 0x10FFEF. ok, but now there is the second problem: how to switch into RM again. have you got any code or tuts? thank you.

http://my.execpc.com/~geezer/osd/index.htm

http://www.mega-tokyo.com/osfaq2/

Only 2 mor to your list

This site as code http://www.karig.net/0004.html

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(@@)
ASHLEY4.

Batteries not included, Some assembly required.

thank you all.
@ashley4: i tried to include the code, but it didn't work! there was always a reboot.

i took out some code to return into RM:

mov eax, cr0
and al, 0xFE
mov cr0, eax

but i don't know, if it works. if i combine both code the kernel doesn't work.
i've already some code to go into PM.

joachim_neu, i have not tested the code my self, so do not no Y it reboots,
but did you click on the "Test code here" link to get the asm code, as the code on the web page is not the full code?.
also remenmber to enable the A20.

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ASHLEY4.

Batteries not included, Some assembly required.

well, i did the misstake, not to put the code into the bootloader! there it works. THANK YOU VERY MUCH! it helped me sooooo much. it's perfect. i may use BIOS-Ints and all of the memory! but i don't find the bad side of the code. what is it? why doesn't everybody use the code? thank you for the answers.

Thank you all very much! Is there a method to test, if i'm realy in PM? my RM-code still works, but i don't know, if i may access all the memory. how may i test it? thank you.

i though again and have an idea. is it, because only the data-register are 32 bit, and not the code-register? so i can use the memory, but i can't execute code in the HMA (High Memory Area)? Thank you.!

Yes thats right.
You can test by writing to a memory loction above 1 MB and reading it back.
The first time i new i was in pmode was when the floppy light stayed on .

NOTE: I do not think BOCHS emulat this mode,so you can not test code with BOCHs, not that i do.

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(@@)
ASHLEY4.

Batteries not included, Some assembly required.

well, if i run my os in bochs, it runs, but i didn't test the writing in the part above 1 MB. i'll test it and write again.

it runs as it should. thank you all!

Hello everybody! here i'm again! with a new problem...


the first part till ;INT 0x67-0x07 should transfair a page into the memory to 0x10000 offset. the second part should transfair the page from 0x10000 offset into the memory again. every page is 0x80000 bytes long, so the parts should copy the page into the CXth page. thatfore i first multiplicate cx with 8 by shl ax,3. if i shl then with 20 i multiply it with 0x10000. then i should have the offset. then i add 0x120000 because at 0x1A0000 starts the first page. therefore i add 0x12 to the number before multiplying it with 0x10000. therefore is the following code:

after that i load the esi- and edi-register with the offsets and set the segments up to 0x00. following i copy 0x40000 words = 0x80000 bytes and then should the page be copied... now about my problem: all that doesn't work. i hope you can help me!

thank you!