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Laaca

Czech republic,
14.08.2021, 07:31

How to keep resident only a part of the program (Developers)

I am thinking about very tiny resident utility which hooks the INT16 interrupt. I know that "high-level" languages like pascal or C have something like function Keep (which apparently calls INT21h/AH=31h). But this function keep a whole program in memory.
My problem is that the program must be quite big and complex (it performs some hardware detections and scanning). But after gathering all needed informations is possible to keep in memory only very small module.
All examples about KEEP function look similarly:

{ Keep.PAS } {$M $800,0,0 } { 2K stack, no heap } { This program makes a click after each keypress.} uses Crt, Dos; var KbdIntVec : Procedure; {$F+} procedure Keyclick; interrupt; begin if Port[$60] < $80 then { Clicks after keypress } begin Sound(5000); Delay(1); Nosound; end; inline ($9C); { PUSHF -- Push flags } { Call old driver } KbdIntVec; end; {$F-} begin { Insert into interrupt chain } GetIntVec($9,@KbdIntVec); SetIntVec($9,Addr(Keyclick)); Keep(0); { Teminate and keep resident } end.

This program works but it remains all int the memory. I would like to keep only the procedure KeyClick but nothing more.

Is possible solution to allocate a additional memory block via INT21h/AH=48h, copy the code of KeyClick into this block and the program end not with Keep but hith Halt?

---
DOS-u-akbar!

tkchia

14.08.2021, 08:49
(edited by tkchia, 14.08.2021, 09:02)

@ Laaca

How to keep resident only a part of the program

Hello Laaca,

> I am thinking about very tiny resident utility which hooks the INT16
> interrupt. I know that "high-level" languages like pascal or C have
> something like function Keep (which apparently calls INT21h/AH=31h). But

Actually the int 0x21, ah = 0x31 interface does allow one to specify how many paragraphs of memory one wants to keep resident. Turbo C and Watcom C also accept a paragraph count as a parameter to keep(...) and (respectively) _dos_keep(...).

But it might be hard to use this correctly in the context of high-level code. You need to arrange your program binary code in such a way that the resident portions will come before (most of) the transient portions (and you must take library functions into account too...). I am not sure what features Free Pascal (e.g.) has that might facilitate this sort of thing.

> Is possible solution to allocate a additional memory block via
> INT21h/AH=48h, copy the code of KeyClick into this block and the program
> end not with Keep but hith Halt?

That will likely not work --- DOS will free up all memory blocks allocated by your program, including those from int 0x21, ah = 0x48.

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

Laaca

Czech republic,
14.08.2021, 10:32

@ tkchia

How to keep resident only a part of the program

> Actually the int 0x21, ah = 0x31 interface does allow one to specify how
> many paragraphs of memory one wants to keep resident. Turbo C and Watcom C
> also accept a paragraph count as a parameter to keep(...) and
> (respectively) _dos_keep(...).
>
> But it might be hard to use this correctly in the context of high-level
> code.

Exactly. I saw in documentatin that INT 21h/AH=31h has a parameter "number of parameters to keep resident" but I don't know how to use it in the pascal code. BTW, in pascal has the Keep function only argument for the return code.

But I know that many assembler programs CAN do it. They use the INT 21h/AH=31h call and determine which portion of code to thow away and which to keep? Or they use some other mechanism?

---
DOS-u-akbar!

tom

Germany (West),
14.08.2021, 11:40

@ Laaca

How to keep resident only a part of the program

> But I know that many assembler programs CAN do it. They use the INT
> 21h/AH=31h call and determine which portion of code to thow away and which
> to keep? Or they use some other mechanism?

usually, you arrange your code layout 'manually' like

resident_code
resident_stuff
transient_code
more_stuff

and make sure that resident_stuff never calls anything in more_stuff after going resident. in ASM this easy, in C at least doable.

for a PASCAL example, you might look at the sources of FreeDOS KEYB.EXE hich I think is written in (some strange sort of) Pascal.

RayeR

CZ,
14.08.2021, 15:49

@ tom

How to keep resident only a part of the program

> and make sure that resident_stuff never calls anything in more_stuff after
> going resident. in ASM this easy, in C at least doable.

I see problem there when resident code would call anything from runtime library that would be freed then. To avoid this probably the best to write TSR part in inline ASM or check compiled code if TSR part doesn't have any depencies.

---
DOS gives me freedom to unlimited HW access.

Laaca

Czech republic,
14.08.2021, 20:18

@ RayeR

How to keep resident only a part of the program

> I see problem there when resident code would call anything from runtime
> library that would be freed then. To avoid this probably the best to write
> TSR part in inline ASM or check compiled code if TSR part doesn't have any
> depencies.

It is no problem at all. I plan to write the TSR part in inline assembler.

But I am considering another attitude. At first to load tiny assembler driver hooking the keyboard interrupt. Then to call a heavy pascal program which will locate the TSR module in memory and patch the code. (kind of self-modyfying code)

---
DOS-u-akbar!

RayeR

CZ,
16.08.2021, 03:22

@ Laaca

How to keep resident only a part of the program

> But I am considering another attitude. At first to load tiny assembler
> driver hooking the keyboard interrupt. Then to call a heavy pascal program
> which will locate the TSR module in memory and patch the code. (kind of
> self-modyfying code)

Yes, it could be possible but you will have to fit in preallocated space. Maybe you can allocate more at the beginning and then free memory that is not longer needed but it will cause some fragmentation.

---
DOS gives me freedom to unlimited HW access.

tom

Germany (West),
14.08.2021, 11:28

@ tkchia

How to keep resident only a part of the program

> Hello Laaca,
>
> > I am thinking about very tiny resident utility which hooks the INT16
> > interrupt. I know that "high-level" languages like pascal or C have
> > something like function Keep (which apparently calls INT21h/AH=31h). But
>
> Actually the int 0x21, ah = 0x31 interface does allow one to specify how
> many paragraphs of memory one wants to keep resident. Turbo C and Watcom C
> also accept a paragraph count as a parameter to keep(...) and
> (respectively) _dos_keep(...).
>
> But it might be hard to use this correctly in the context of high-level
> code. You need to arrange your program binary code in such a way that the
> resident portions will come before (most of) the transient portions (and
> you must take library functions into account too...). I am not sure what
> features Free Pascal (e.g.) has that might facilitate this sort of thing.
>
> > Is possible solution to allocate a additional memory block via
> > INT21h/AH=48h, copy the code of KeyClick into this block and the program
> > end not with Keep but hith Halt?
>
> That will likely not work --- DOS will free up all memory blocks
> allocated by your program, including those from int 0x21, ah = 0x48.

while true (this wouldn't work), you can make it work by using the undocumented feature that DOS_realloc(para, size) also sets the PSP of the allocated memory, and on exit(), DOS will only free allocated memory with your PSP.

so a sequence like

needed_bytes = 1024;

resident_seg = DOS_alloc(needed_bytes);

my_PSP = DOS_GET_PSP();

DOS_SET_PSP(0x60); program 0x60 will never exit

DOS_realloc(resident_seg, needed_bytes);

DOS_SET_PSP(my_PSP);

memcpy(MK_FP(resident_seg,0), my code, needed_bytes);

point interrupt vector to the copied code
...

exit()

would work in principle (remove the large program from memory, leave needed_bytes in memory).

of course, your code would really quickly implode because you are calling the runtime library (sound(), delay()) and you have little to no control over where the runtime will be loaded.

time to change the language :-D

Pascal is just not the right language for this kind of stuff.

ecm

Düsseldorf, Germany,
15.08.2021, 13:47

@ tkchia

How to keep resident only a part of the program

> > Is possible solution to allocate a additional memory block via
> > INT21h/AH=48h, copy the code of KeyClick into this block and the program
> > end not with Keep but hith Halt?
>
> That will likely not work --- DOS will free up all memory blocks
> allocated by your program, including those from int 0x21, ah = 0x48.

You can make it work by hacking the MCB to be owned by someone other than your process. Tom mentions a way to do that but I think it is cleaner to just access the MCB directly instead of setting the current PSP to another, possibly invalid value.

In my tsr example I first relocate the process (to avoid memory fragmentation) then allocate a new block for the resident portion using service 48h, then I hack the MCB's owner and name fields to make the resident block survive the final process termination (using service 4Ch). I described this in some detail in https://retrocomputing.stackexchange.com/questions/20001/how-much-of-the-program-segment-prefix-area-can-be-reused-by-programs-with-impun/20006#20006

By the way, if you do use service 31h you should close all file handles manually, unless you intend to use them while resident.

---
l

bretjohn

Rio Rancho, NM,
27.08.2021, 21:22

@ ecm

How to keep resident only a part of the program

I use ecm's TSR installation method (or at least a slight variation of it) in most of my TSR's nowadays. It works really well. It even allows you to automatically install the program into upper memory without needing to use LOADHI. I'm not sure you could do it (at least not easily) in anything other than ASM, though. ASM is more difficult to use, but can give you complete control over everything, including the relationships of which parts of the program get installed in which parts of memory.

I will say that INT 21.31 is probably the easiest way to install a TSR, but it is not the best option (by far).

marcov

14.08.2021, 13:18

@ Laaca

How to keep resident only a part of the program

> I am thinking about very tiny resident utility which hooks the INT16
> interrupt. I know that "high-level" languages like pascal or C have
> something like function Keep (which apparently calls INT21h/AH=31h). But
> this function keep a whole program in memory.
> My problem is that the program must be quite big and complex (it performs
> some hardware detections and scanning). But after gathering all needed
> informations is possible to keep in memory only very small module.
> All examples about KEEP function look similarly:

Did you walk through the TSR section of SWAG ?

CandyMan

27.08.2021, 17:46

@ Laaca

How to keep resident only a part of the program

If you want to write resident programs then use assembler. Here is my old program, replacement for the DOS keyboard driver, written in fasm. The resident part is between KeyStart and KeybSize.
Here code:
org 100h mov dx,Information+1 call Print mov ax,3509h int 21h mov word [KeyStart+Old09h+0],bx mov word [KeyStart+Old09h+2],es mov ah,$AD ; Disable Controller call SetStat in al,21h ;\ or al,00000010b ; > Disable IRQ1 out 21h,al ;/ mov ah,20h ; Read Command Byte call GetEcho push ax mov ah,$AA ; Keyboard Self Test call GetEcho jnz NotAnswer cmp al,55h jnz NotAnswer mov ah,$F4 ; Enable Keyboard call SetOut mov ah,$F3 ; Set Typematic Rate&Delay call SetOut mov ah,0 ; Max Rate&Delay call SetOut NotAnswer: pop bx ; Restore Command Byte or bl,1 mov ah,60h ; Set Command Byte call SetEcho mov ah,$AE ; Enable Controller call SetStat in al,21h ;\ and al,11111101b ; > Enable IRQ1 out 21h,al ;/ call GetMem jc Quit xor di,di mov cx,KeybSize mov si,KeyStart rep movsb push es pop ds mov ax,2509h mov dx,New09h int 21h ret Quit: mov dx,NoMem Print: mov ah,9 int 21h ret Allocate: mov ah,48h mov bx,Paragraphs int 21h ret GetMem: mov ax,5802h int 21h xor ah,ah mov si,ax cmp al,1 je LoadUpper mov ax,5803h mov bx,1 int 21h jc NoUpper LoadUpper: call Allocate pushf push ax mov ax,5803h mov bx,si int 21h pop ax popf jnc IsOK NoUpper: mov ah,4Ah mov bx,-1 push ds pop es int 21h sub bx,Paragraphs+1 jc MemEnd mov ah,4Ah int 21h jc MemEnd call Allocate jc MemEnd IsOK: push ax dec ax mov es,ax inc ax mov di,1 cld stosw add di,5 mov si,Information movsw movsw movsw movsw pop es MemEnd: ret ; Wait Not Data in port 60h\64h WaitNoData: xor cx,cx .WaitRetry: in al,64h out $EB,al test al,00000010b jz .Ok loop .WaitRetry inc cx .Ok: ret ; Wait No TimeOut (Data transmit completed) WaitNoTime: xor cx,cx .WaitTime: in al,64h test al,00100000b jz .Ok loop .WaitTime inc cx .Ok: ret ; Wait Data in port 60h WaitOutput: mov ah,0Ch .CheckAgain: xor cx,cx .CheckOutput: in al,64h out $EB,al test al,00000001b jnz .IsOutput ; Ok! loop .CheckOutput dec ah ; \ Wait error! jnz .CheckAgain ; / Wait again .IsOutput: lahf ; \ xor ah,40h ; > Negate ZF sahf ; / ret ; Set Command in AH to Status Register SetStat: cli call WaitNoData jnz .Err mov al,ah out 64h,al call WaitNoData .Err: sti ret ; Set Command in AH to Output Register SetOut: cli call WaitNoTime jnz .Err in al,60h call WaitNoData jnz .Err mov al,ah out 60h,al call WaitNoData call WaitOutput jnz .Err in al,60h cmp al,$FA .Err: sti ret ; Set Command in AH to Status Register & ; get echo\command from Output Register GetEcho: cli call SetStat jnz .Err call WaitOutput jnz .Err in al,60h .Err: sti ret ; Set Command in AH to Status Register & ; set echo\command in BL from Output Register SetEcho: cli call SetStat jnz .Err call WaitNoData jnz .Err mov al,bl out 60h,al call WaitNoData .Err: sti ret ReadInput: cli mov bx,$FF0F call WaitNoData jnz .Err .Retry: mov ah,$C0 call GetEcho jnz .Err cmp al,bh je .Ok mov bh,al xor cx,cx loop $ dec bl jnz .Retry .Err: inc cx .Ok: sti ret Information db '$KEYB-PL v1.1',13,10,36 NoMem db 13,10,'Not enough memory',13,10,36 KeyStart: org 0 KeyTable: db $1E,$2E,$12,$26,$31,$18,$1F,$2C,$2D db $A5,$86,$A9,$88,$E4,$A2,$98,$BE,$AB db $A4,$8F,$A8,$9D,$E3,$E0,$97,$BD,$8D New09h: push ax bx ds si push 40h pop ds mov ax,[1Ch] mov si,ax inc ax inc ax cmp ax,[82h] jne @1 mov ax,[80h] @1: cmp ax,[1Ah] je Return xchg bx,ax mov ax,[17h] test al,8 je Return xchg ah,al test al,2 jne Return in al,60h cmp al,31h ; Max z KeyTable ja Return push di push cx push es push cs pop es cld mov cx,9 xor di,di ; mov di,KeyTable repnz scasb pop es pop cx jne Exit xchg ah,al test al,40h je @2 and al,3 ; test al,3 jne @4 jmp @3 @2: and al,3 ; test al,3 je @4 @3: add di,9 @4: cbw ; xor ah,ah mov al,[cs:di+8] mov [si],ax mov [1Ch],bx mov al,20h out 20h,al pop di si ds bx ax iret Exit: pop di Return: pop si ds bx ax db $EA Old09h dd ? KeybSize: Paragraphs = ($+15)/16

bretjohn

Rio Rancho, NM,
27.08.2021, 21:47

@ Laaca

How to keep resident only a part of the program

From a performance perspective, this would not be a good way to implement a keyclick program. You have the sound being turned on, waiting, and turning off all inside an INT 09 (hardware IRQ) handler, which is not a good idea. The keyboard is a very high priority IRQ (the only one being higher is the clock at INT 08) and the machine will "stall" inside the IRQ 09 handler waiting for the sound to stop. This could cause some serious performance issues in other programs.

There are a few different ways around this. What may be the easiest/best in this situation would be to simply start the sound within the INT 09 handler and then stop it after a delay using one of the timer interrupts (INT 08 or INT 70h).

Laaca

Czech republic,
08.03.2022, 12:24

@ Laaca

How to keep resident only a part of the program

I succeeded to solve this problem!
It is possible to create a big program in the Turbopascal and keep only a tiny TSR in the memory and unloaded the rest.
The practical implementation I used here.

The principle is to write a small assembler procedure which will be used as a TSR. In this procedure keep a area which will be modified on the fly to store there some data.
Then move this procedure/module just after PSP of the main program. (PSP+256)
Now is it a little bit dangerous because a part of the pascal system library is overwritten so it is not safe to call many RTL functions.
In assembler redirect the calling interrupt vector to PSP+256
Then call the DOS function 31h and into DX store the 16+TSR_size/16.
And it works :-)

The question is: Do I need to keep the PSP? Is it safe to perform the relocation not to PSP+256 but to PSP+128? Or to PSP+0?

---
DOS-u-akbar!

tom Germany (West), 08.03.2022, 12:51 @ Laaca	How to keep resident only a part of the program Post reply
	> The question is: Do I need to keep the PSP? yes, at least part of it is used on exit() 'terminate program' lime parent PSP, INT 23 address and similar. > Is it safe to perform the > relocation not to PSP+256 but to PSP+128? Or to PSP+0? PSP+80 should be enough as you probably don't use FCB's, and have used your command line (@PSP+128) a long time ago.

tkchia

08.03.2022, 14:20

@ tom

How to keep resident only a part of the program

Hello Laaca, hello tom,

> > Is it safe to perform the
> > relocation not to PSP+256 but to PSP+128? Or to PSP+0?
> PSP+80 should be enough as you probably don't use FCB's, and have used your
> command line (@PSP+128) a long time ago.

Actually, if the program does not use FCBs, one can probably throw away everything above PSP:0x5c (where the first default FCB starts).

(Or perhaps even everything above PSP:0x50. There is a "int 0x21; retf" sequence at PSP:0x50, but other than that there is nothing between PSP:0x50 and PSP:0x5c.)

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

bretjohn

Rio Rancho, NM,
08.03.2022, 19:19

@ tkchia

How to keep resident only a part of the program

As far as to how much of the PSP you need to keep after the TSR is installed, the answer is usually 0. Except in very rare cases, the PSP is only used while the TSR is being installed but is not used by the TSR itself. So, you can overwrite the PSP with whatever you want. I've used the PSP for various different things in my TSR's, the most useful probably being as a TSR Stack (complicated TSR's should always provide their own stack space).

You do need to make sure you don't overwrite the PSP before the TSR is actually installed, though. That can be a little tricky in high-level languages like Pascal since you don't necessarily know exactly when or how the PSP is used.

rr

Berlin, Germany,
08.03.2022, 17:32

@ Laaca

How to keep resident only a part of the program

> I succeeded to solve this problem!

:yes:

> It is possible to create a big program in the Turbopascal and keep only a
> tiny TSR in the memory and unloaded the rest.
> The practical implementation I used here.
>
> The principle is to write a small assembler procedure which will be used as
> a TSR. In this procedure keep a area which will be modified on the fly to
> store there some data.
> Then move this procedure/module just after PSP of the main program.
> (PSP+256)
> Now is it a little bit dangerous because a part of the pascal system
> library is overwritten so it is not safe to call many RTL functions.
> In assembler redirect the calling interrupt vector to PSP+256
> Then call the DOS function 31h and into DX store the 16+TSR_size/16.
> And it works :-)

A bit late, because you already solved it, but https://github.com/FDOS/keyb might be of interest.

---
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