VOGONS

Search

Common searches

On Sound Blaster Direct Dac and Mixer Control

Topic actions

First post, by wuerzig

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Hi there,

I have some old turbo pascal code which makes use of the so-called "direct-dac" and mixer control feature of SB cards a lot. It essentially is a mixer (as in windows mixer) application to control the sb16's channels volume (master, voice, midi, cd, line-in), and the cd-audio colume of mscdex. In addition to that, it uses sampling via direct-dac to display the recording volume. It can also control the playing of cd-audio.

The cd-audio code works since dosbox 0.71 (thanks btw 😀) . However, neither the code to control the sb's channels volume (simply does nothing), nor the code to aquire samples from the sound card work (hangs on waiting for input).

I can imagine the emulation simply doesnt go that far and the features havent been added to dosbox yet. Maybe my code just sucks, I was kinda young at the time 🤣

I can supply code samples or the source of the whole app if you need more concrete examples.

Thanks in advance for any replies,

Thomas

Reply 1 of 2, by Qbix

Posted on 
User metadata
Rank DOSBox Author
Rank
DOSBox Author

the mixer should be functional. at least it works in games 😀
You could post some code samples if you want. Preferable samples as the whole source will be a lot to read through.

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

Reply 2 of 2, by wuerzig

Posted on 
User metadata
Rank Newbie
Rank
Newbie

After a bit of testing the master, voice and midi channels now work (tweaked one line of code), tho not as my old puter handled it. While playing cd or feeding it something via line-in, the master volume controlled the overall volume of sound. I guess dosbox doesnt route the cd-audio through its emulated sound device and thus the control of that volume is impossible.

-- Code samples (Turbo Pascal... $ means Hex like 0x in C, comments in {})

procedure SetMSCDEXVolume(Vol : Byte;cdr:word); assembler;
asm
      mov			bx,seg Req                    
      mov			es,bx                           
      mov			bx,offset Req                 
      mov			byte ptr es:[bx+2],0Ch            
      mov			cx,cdr                       {drive letter}
      mov			byte ptr ioctl,03h                {function}
      xor			al,al                             {start at channel 0}
      mov			ah,Vol                            {volume - user input}
      mov			word ptr ioctl+1,ax               {left}
      inc			al                                {next channel}
      mov			word ptr ioctl+3,ax               {right}
      inc			al                                {next channel}
      mov			word ptr ioctl+5,ax               {left prime}
      inc			al                                {next channel}
      mov			word ptr ioctl+7,ax               {right prime}
			mov			word ptr es:[bx+0Eh],offset ioctl {transfer offset}
      mov			word ptr es:[bx+10h],seg ioctl    {transfer segment}
      mov			ax,1510h                          {mscdex service}
      int			2Fh                               {send device driver request}
end;

function GetMSCDEXVolume(cdr:word) : Byte; assembler; 
asm
      mov			ax,1510h                          {mscdex service}
      mov			bx,seg Req                    
      mov			es,bx                             
      mov			bx,offset Req                 
      mov			byte ptr es:[bx+2],03h            {command code}
      mov			cx,cdr                       {drive letter}
      mov			byte ptr ioctl,04h                {function}
			mov			word ptr es:[bx+0Eh],offset ioctl {transfer offset}
      mov			word ptr es:[bx+10h],seg ioctl    {transfer segment}
      int			2Fh                               {send device driver request}
      mov			al,byte ptr ioctl+2               {result - left chn's volume}
end;

And for direct-dac:

      RESETPORT=$226;
      READPORT=$22A;
      WRITEPORT=$22C;
      STATUSPORT=$22C; { its odd that these two have the same value, but the code worked on a real machine}
      DATADAPORT=$22E;


function resetDSP:boolean;
var maxv:byte;
    drw:byte;
begin
  maxv:=100;
  drw:=0;
  while (drw<>$AA) and (maxv<>0) do begin
    port[RESETPORT]:=1;
    delay(10); { waits 10 milliseconds }
    port[RESETPORT]:=0;
    drw:=readfromDSP;
    dec(maxv); { maxv-- }
  end;
  if maxv=0 then resetDSP:=FALSE
  else resetDSP:=TRUE;
end;

procedure write2DSP(command:byte);
begin
  while ((port[STATUSPORT] and $80)<>0) do ;
  port[WRITEPORT]:=command;
end;

function readfromDSP:byte;
begin
  while ((port[DATADAPORT]and $80)<>$80) do ;{<-- hangs here <-- }
  readfromDSP:=port[READPORT];
end;

{ samples can then be aquired this way: }
if not resetDSP then fail;
while weWantSamples do begin
    write2DSP($20);
    sample:=readfromDSP;
end;


Go to top of page Go to top of page
Back to DOSBox Development
Close window
Close window