Dos INT 21h function 1 does not echo \ VOGONS

Dos INT 21h function 1 does not echo

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First post, by verelse

Posted on 2009-02-26, 17:16

verelse Offline

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Int 21h function 01h does not echo input characters to the console. I built the attached TASM code using Turbo Assembler 5.0 under DOSBox 0.72 on these machines:

Dell D630, Windows XP 64 bit, sp3, 4GB RAM, Quadro NVS 135 128MB.
Dell Precision 490, Dual Xeon Dual-Core 3.2, 24GB RAM, Vista 64-bit
Dell GX270 P4 HT, 2GB DDR2 RAM, Intel GMA cruddy video card

Got same results, no echo from function 1 int 21h. Compiled under MS-DOS 6.22 running on Compaq Deskpro XL Pentium Pro 200 MHz with 64MB RAM, under MS-DOS 6.22 on VMWare Workstation 6 and Virtual PC 7 got correct results, echo'd characters from function 1.

I am aware I can workaround this, but this function is fairly integral to DOS and was even inherited from CP/M if I remember rightly.
Can't seem to get attachment to work so including code below.

1
2;-------------------------------------------------------------------- 
3;   program:        echoout 
4;   function:       reads until nothing left or eof char
5;   owner:          *****
6;   date:           changes 
7;   1998/04/15      original version 
8;-------------------------------------------------------------------- 
9          ideal                        ;use turbo ideal mode 
10          model      small             ;64k code and 64k data 
11          p8086                        ;only allow 8086 instructions 
12          stack      256               ;reserve 256 bytes for the stack 
13;--------------------------------------- 
14          dataseg                       ;start the data segment 
15;--------------------------------------- 
16eof_char  db         1ah               ;byte variable dos eof char
17;--------------------------------------- 
18         codeseg                       ;start the code segment 
19;--------------------------------------- 
20start:                                 ; 
21         mov          ax,@data         ;establish addressability to the 
22         mov          ds,ax            ;data segment for this program 
23;--------------------------------------- 
24; do the dew before the dew does you
25;--------------------------------------- 
26dowhile: mov      ah,0bh               ;set int 21h function check buffer
27         int      21h                  ;check for character in stream
28         cmp      al,00h               ;check for lack of data
29         je       exit                 ;term on no data
30         mov      ah,01h               ;set int 21h function read w echo
31         int      21h                  ;ask dos for character from stream
32         cmp      al,[eof_char]        ;is character eof?
33         je       exit                 ;term on eof character
34         jmp      dowhile              ;
35;--------------------------------------- 
36; terminate program execution 
37;--------------------------------------- 
38exit:                                  ; 
39         mov      ax,4c00h             ;set dos code to terminate  
40         int      21h                  ;return to dos 
41         end      start                ;mark the end of the source code 
42                                       ;....specify start execution
43;--------------------------------------- 
44
45

Reply 1 of 6, by wd

Posted on 2009-02-26, 17:59

wd Offline

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There's echo code present at int21/1 which looks fine. Can you please post the assembled file? (zip it when attaching it)

Reply 2 of 6, by ripsaw8080

Posted on 2009-02-26, 18:16

ripsaw8080 Offline

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The way this program is written seems to imply redirected input (e.g. echoout < somefile) because it will immediately exit if there is no input pending (INT 21/0B). I tried it, and INT 21/01 is not echoing under redirected input, however it does echo without redirected input (typing on the keyboard).

Reply 3 of 6, by wd

Posted on 2009-02-26, 18:23

wd Offline

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Right, echo works only when the input is the console as the echoing is handled in the con device in dosbox.

Reply 4 of 6, by Qbix

Posted on 2009-02-26, 18:26

Qbix Offline

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I think no game relies on that echo thing through redirection. So I can live with it.

Water flows down the stream
How to ask questions the smart way!

Reply 5 of 6, by verelse

Posted on 2009-02-26, 19:02

verelse Offline

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You are right, the code is designed to work with redirected input, con works fine, I should have been more clear.
Int 21h 01h is not a console function, it is an input function and it should work with redirected input. I imagine you are right, no games need this functionality at least from redirect. I just noticed it building some assembler libraries in DOSBox that long used code did not work. DOSBox is not just for games, though, or is it?
I can modify my lib by reading without echo then writing the character, in other words just manually echoing input. I am sure I am out of the ordinary in wanting to do something besides play games with DOSBox. I use it to run legacy code on x64 Windows systems, but I can go back to VMWare. DOSBox is just so fast and friendly and sharing the same file system is sweet.

Thanks for your time, guys.

Reply 6 of 6, by wd

Posted on 2009-02-26, 19:24

wd Offline

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The only aim for dosbox development is games, of course this does not mean it only runs dos games.

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