The Benefits of Dedicated Hardware Acceleration for Audio

                      Monster Sound and Input Devices
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This document attempts to clear up some of the confusion surrounding the
Monster Sound digital joystick issue. In order to do this we need to look
at the characteristics of the two fundamental components in question, the
input device (joystick, game pad, etc...), and the Monster Sound gameport.

Input Devices
Input devices (including joysticks, game pads, flight yokes, etc...)
designed to use the PC gameport typically come in one of two flavors:
analog or digital. Currently most input devices for the PC are analog only.
Recently some digital only devices, such as the SideWinder gamepad, have
been introduced to the market. Additionally some hybrid devices, such as
the SideWinder 3D Pro joystick, support both analog and digital modes.

Analog Devices
Analog input devices incorporate capacitor/potentiometer circuits to
indicate the x/y/z position information. As the joystick is moved, the
charge/discharge characteristics of the analog lines change. When attached
to an unaccelerated gameport, the DOS application or Windows driver must
constantly poll the gameport watching for transitions in the state of the
analog lines in order to interpret the joystick position. This polling uses
precious CPU cycles.

Digital Devices
Digital input devices typically incorporate microprocessors and/or other
circuitry that interpret the joystick position digitally. In order to work
over the PC gameport, manufactures of these devices have devised
proprietary schemes for transmitting the digital information over the
gameport lines. For this reason, direct support for the device must be
built into the DOS application or Windows driver. Often the input device
driver will communicate directly with the gameport hardware, thus bypassing
or replacing the Monster Sound gameport driver, as well as other Windows
only sound card drivers.. This need for direct access is largely due to the
performance requirements imposed by the proprietary digital protocol, and
the need to communicate with the port in ways not supported by DirectInput
and the standard polled gameport driver.

The perceived advantage of digital devices over analog is their improved
resolution (accuracy) and the capacity to support more features (more
buttons, sliders, axis, etc...). Depending on the characteristics of the
proprietary digital protocol, communication with the device MAY be more
efficient (use less CPU) than polled analog devices.

Monster Sound GamePort
The Monster Sound gameport operates in one of two modes: accelerated or
compatibility.

Accelerated Mode
In accelerated mode, the Monster Sound hardware performs the polling
operation. This alleviates the need for the application/driver to poll the
gameport, thus reducing CPU overhead. In Windows, the Monster Sound
gameport driver reports back the positional information via the Direct
Input API.

The Monster Sound gameport operates in accelerated mode when an analog
device is attached. The gameport driver works in concert with Direct Input
to relay accelerated position/state information to the application in a
hardware independent fashion via the Direct Input API.

Compatibility Mode
In compatibility mode, the Monster Sound gameport operates like a standard
legacy gameport. In this mode an application or driver must poll the
Monster Sound gameport much as it would a standard gameport.

The Monster Sound gameport is switched to compatibility mode when a digital
device is attached. This is because the driver for the input device
typically wants to access the gameport directly, thus bypassing the Monster
Sound gameport driver. In compatibility mode the Monster Sound gameport
must respond and look like a legacy gameport, which it does. The problem
is, because Monster Sound, as well as most other new audio cards, are PCI
devices the gameport does not appear at the ISA legacy gameport address of
0x201. Unfortunately most digital input drivers look for the game port at
this hard-coded address.

There are two solutions to this problem. The first and more short term
solution is to modify the input device driver to query for, and
subsequently use, the Monster Sound gameport. The second and longer term
solution is to add the necessary support in the operating system
(DirectInput) so the input device driver can communicate with the gameport
in a more hardware independent manner. The short term fix has been
implemented for almost all new digital devices (see section on resolution)
and Microsoft has publicly committed to helping resolve this issue in their
next OS (Windows 98) scheduled to release early in 1998.

Conclusion
When an analog input device is attached to the Monster Sound, the gameport
and driver operate in accelerated mode. Most, if not all, analog devices
should be compatible with Monster Sound in this scenario, and should reap
the benefits of Monster Sounds gameport acceleration. Likewise, hybrid
devices will typically fall back to analog mode and also work compatibly
with Monster Sound's accelerated gameport.

Pure digital devices require either a workaround in the input device driver
to work with Monster Sound's gameport, or must support the Direct Input
modifications planned for future releases of Windows.
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