## Using The DOSEMU Sound System (SBEMU)

Alistair MacDonald,

<A.MacDonald@slitesys.demon.co.uk>

dosemu-1.0

The document describes the use of the DOSEMU Sound code (SBEMU), and what you can expect from it.

## Introduction

It is much better to be pessimistic about the capabilities of DOSEMU's sound code. The code itself provides an EMULATION of the popular SB cards. The actual level of emulation that can be achieved is dependant upon the capabilities of the sound driver on your system. Currently the emulation can only talk to the OSS driver (included in the Linux kernel) although it has been written in a modular fashion to allow other drivers to be written. For more details on the internals please see the WWW pages at http://www.slitesys.demon.co.uk/a.macdonald/dosemu/sound/.

It should be pointed out that not all of this information comes from my own knowledge and that parts come from the other developers and from users who have contributed code & comments. Unfortunately I tend to forget names and lose emails, so their names are not included.

## What to (and what not to!) expect

The emulation consists of a number of parts, and I'll examine these separately.

### FM

The FM driver is the least complete. Most of the chip functions are there, but no audio output occurs. This means that software which uses the presence/operation of the timer should detect the timer presence, but if the audio needs/uses FM you will hear nothing.

#### Technical Explanation

There are a number of problems with the FM emulation:

1. Any FM output will have to be translated to appropriate OSS sequencer calls. These vary according to the SoundCard family (mainly between the cards with real FM synthesis and those with wavetable synthesis) You actually need to detect the card type and program it accordingly.

2. The OSS sequencer doesn't allow you to change the parameters whilst a note is playing. Many games do this to provide their sound.

### MPU-401

This is the MIDI emulation. This should be fairly complete, but relies on the external daemon 'midid'. This is supplied and can be built easily.

### SB (Digital)

This is the digital aspect of the audio output. It is the most mature, and also the buggiest aspect (because it is the most complex!) Most of the functionality up to SB-16 is implemented, although some things don't work. Note that SB (DSP) MIDI is not implemented, although MPU-401 emulation (above) is.

### DMA

Whilst technically not part of the Sound System, the DMA emulation routines where developed primarily for SBEMU. These routines may have their own problems which may well impact on the running of SBEMU. As far as we know the only limitation is that they don't interface with the real DMA controller.

## Using SBEMU

SBEMU needs to be compiled into DOSEMU, AND turned on at run-time. Then your DOS applications need to be configured to use the emulation. (Just as they need to be configured to use your real sound card). The basic steps are given below.

### DOSEMU Compile-time Configuration

By default, DOSEMU is built with SBEMU support.

### DOSEMU Run-time Configuration

The default settings are:

        Base Address:   220
        IRQ:            5
        DMA:            1
        Midi Port:      330 (Not normally needed)

Note that these do NOT need to be the same as your real sound card.

#### Changing the SBEMU settings

The DOSEMU Sound settings are controlled by the following entries in `/etc/dosemu.conf` Note that there is some overlap here with the configuration notes in the README. This will be addressed at a later stage :

    $_sound = (off)		# sound support on/off
    $_sb_base = (0x220)
    $_sb_irq = (5)
    $_sb_dma = (1)
    $_sb_dsp = "/dev/dsp"
    $_sb_mixer = "/dev/mixer"
    $_mpu_base = "0x330"

Note that these are the default values. `$_sb_dsp` and `$_sb_mixer` are pre-configured to work with the standard OSS-Free driver. You are unlikely to need to change these values unless you have multiple drivers in your kernel.( eg such as the Ultra project drivers).

#### Configuring Midi

The midi driver can be used in two way. It is possible to direct the output of the SBEMU midi driver directly to a sound card, or through the `midid` daemon. All midi traffic is directed at `~/.dosemu/run/dosemu-midi`. You will need to create this, or link it to the appropriate device, according to your configuration. Details about this are given below.

##### Using Midid

This is the preferred method of producing MIDI output. The `midid` is NOT built at the same time as DOSEMU, but it is simple to build:

    % make midid

This will create `src/arch/linux/dosext/sound/midid/midid`. You will probably want to copy this somewhere on your path, such as `/usr/bin`. Next you will need to create the output pipe for the SBEMU driver:

    % mkdir -p ~/.dosemu/run
    % rm -f ~/.dosemu/run/dosemu-midi
    % mknod ~/.dosemu/run/dosemu-midi p

If you already have a `~/.dosemu/run` directory then the `mkdir` will fail. This is not a problem.

Finally, you need to start the midid program:

    % midid < ~/.dosemu/run/dosemu-midi &

This will run the driver in the background, giving you your prompt back.You should now run DOSEMU. Midid will terminate when DOSEMU terminates.

Note that midid currently only supports the Ultra driver (autodetected when DOSEMU is configured), OSS/Free (partially) and a NULL driver (which just outputs the data stream as text). Midid should detect which is applicable. Running midid with the argument `-h` will list the options.

##### Sending Midi direct to a device

This will ONLY work if your Midi device accepts raw midi data and you have either preloaded instruments patches, or it has hardware patches. Use this method ONLY if you cannot use the previous method, and do not EXPECT support.

To use this method you simply need to link the SBEMU midi output file to the input of your MIDI device. The simplest method of doing this is:

    % mkdir -p ~/.dosemu/run
    % rm -f ~/.dosemu/run/dosemu-midi
    % ln -s /dev/MyMidiDevice ~/.dosemu/run/dosemu-midi

Where `/dev/MyMidiDevice` is the path to your midi device. If you already have a `~/.dosemu/run` directory then the `mkdir` will fail. This is not a problem.

### Configuring DOS

You should set your BLASTER environment variable to match your DOSEMU settings. Note that these don't need to correspond to your real sound card. For a base SB with the values above, use the following DOS command:

    set BLASTER=A220 I5 D1 T1

The T1 identifies this as a Type 1 SB device eg old! The precise version of 'SB' is up to you, but the lower the model, the more likely it is to work.

### Configuring the Applications

Bearing in mind what was stated above, the following are the recommended methods for configuring applications to use SBEMU. The first is the preferred method. If you need to manually set any parameters remember to use those you configured DOSEMU with.

#### Midi with Digital Audio

Configure the applications to use 'General Midi' for Music, and 'SB' for Digital Audio.

#### SB Music with SB Audio

Configure the application with 'SB' for Music & Audio. Note that if the system plans to use FM for the music you will not get music.

#### Midi Music, No Audio

Configure the application with 'General Midi' for Music and no Audio.

## Debugging SBEMU

The debugging output for SBEMU is enabled in the same way as all DOSEMU debug, and collected in the same manner. The debug flag for sound is 'S'. Because the DMA controller is hardware it uses the debug flag 'h'. To get basic debugging information into a file called `sound.out` use:

    % dos -D-a+Sh -o sound.out

You can get slightly more verbose output is you use level 2 debugging (eg use `-D-a+2Sh`). If you need someone else to look at the debug output then feel free to send it to the list, but PLEASE, remove any unnecessary debug output, and give a DETAILED description of the problem. Ideally, use the bug reporting tool `submit-bug-report`.