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Chapter 6 Audio Subsystem
Compaq Deskpro EN Series of Personal Computers
Desktop and Minitower Form Factors
Third Edition - September 1998
6-8
6.3 PROGRAMMING
All programming aspects of the audio subsystem relate directly to the programmability of the
ES1869 controller, upon which the audio subsystem is based. This section describes only the
basic mapping of the audio functions. For a detailed description of the ES1869s registers and
capabilities refer to the ES1869 AudioDrive Data Sheet, ESS Technology, Inc.
6.3.1 CONFIGURATION
The audio subsystem is automatically configured as to base address, DMA, and interrupts
following installation and power up through an on-board EEPROM that provides Plug ‘n Play
support. Software can identify the ES1869 controller by reading indexed address 2n5.40h
successively (where n = 2 for primary address or 4 for secondary address), which should yield the
values 18h, 69h, followed by the base address of the ES1869.
The typical reset/power-up configuration for the audio subsystem is as follows:
Base Address: 220h
Interrupt: IRQ5
DMA Channel: 1
Power Management: Automatic
The audio subsystem can be configured or either single DMA channel mode or dual DMA
channel mode. Single DMA channel mode means that capture and playback operations share the
same (playback) DMA channel and only one operation, capture
or
playback, is possible at a time.
Dual DMA channel operation allows simultaneous capture/playback (full duplex) operation to
occur if desired, but requires the use of two DMA channels. Typically, dual DMA operation
would use DMA channel 1 for capture (recording) and DMA channel 0 or 3 for playback.