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+ An OSS/Lite Driver for the ESS Maestro family of sound cards
+ Zach Brown, December 1999
+Driver Status and Availability
+The most recent version of this driver will hopefully always be available at
+I will try and maintain the most recent stable version of the driver
+in both the stable and development kernel lines.
+ESS Maestro Chip Family
+There are 3 main variants of the ESS Maestro PCI sound chip. The first
+is the Maestro 1. It was originally produced by Platform Tech as the
+'AGOGO'. It can be recognized by Platform Tech's PCI ID 0x1285 with
+0x0100 as the device ID. It was put on some sound boards and a few laptops.
+ESS bought the design and cleaned it up as the Maestro 2. This starts
+their marking with the ESS vendor ID 0x125D and the 'year' device IDs.
+The Maestro 2 claims 0x1968 while the Maestro 2e has 0x1978.
+The various families of Maestro are mostly identical as far as this
+driver is concerned. It doesn't touch the DSP parts that differ (though
+it could for FM synthesis).
+Driver OSS Behavior
+This OSS driver exports /dev/mixer and /dev/dsp to applications, which
+mostly adhere to the OSS spec. This driver doesn't register itself
+with /dev/sndstat, so don't expect information to appear there.
+The /dev/dsp device exported behaves almost as expected. Playback is
+supported in all the various lovely formats. 8/16bit stereo/mono from
+8khz to 48khz, and mmap()ing for playback behaves. Capture/recording
+is limited due to oddities with the Maestro hardware. One can only
+record in 16bit stereo. For recording the maestro uses non interleaved
+stereo buffers so that mmap()ing the incoming data does not result in
+a ring buffer of LRLR data. mmap()ing of the read buffers is therefore
+disallowed until this can be cleaned up.
+/dev/mixer is an interface to the AC'97 codec on the Maestro. It is
+worth noting that there are a variety of AC'97s that can be wired to
+the Maestro. Which is used is entirely up to the hardware implementor.
+This should only be visible to the user by the presence, or lack, of
+'Bass' and 'Treble' sliders in the mixer. Not all AC'97s have them.
+The driver doesn't support MIDI or FM playback at the moment. Typically
+the Maestro is wired to an MPU MIDI chip, but some hardware implementations
+don't. We need to assemble a white list of hardware implementations that
+have MIDI wired properly before we can claim to support it safely.
+Compiling and Installing
+With the drivers inclusion into the kernel, compiling and installing
+is the same as most OSS/Lite modular sound drivers. Compilation
+of the driver is enabled through the CONFIG_SOUND_MAESTRO variable
+in the config system.
+It may be modular or statically linked. If it is modular it should be
+installed with the rest of the modules for the kernel on the system.
+Typically this will be in /lib/modules/ somewhere. 'alias sound maestro'
+should also be added to your module configs (typically /etc/conf.modules)
+if you're using modular OSS/Lite sound and want to default to using a
+As this is a PCI device, the module does not need to be informed of
+any IO or IRQ resources it should use, it devines these from the
+system. Sometimes, on sucky PCs, the BIOS fails to allocated resources
+for the maestro. This will result in a message like:
+ maestro: PCI subsystem reports IRQ 0, this might not be correct.
+from the kernel. Should this happen the sound chip most likely will
+not operate correctly. To solve this one has to dig through their BIOS
+(typically entered by hitting a hot key at boot time) and figure out
+what magic needs to happen so that the BIOS will reward the maestro with
+an IRQ. This operation is incredibly system specific, so you're on your
+own. Sometimes the magic lies in 'PNP Capable Operating System' settings.
+There are very few options to the driver. One is 'debug' which will
+tell the driver to print minimal debugging information as it runs. This
+can be collected with 'dmesg' or through the klogd daemon.
+The other, more interesting option, is 'dsps_order'. Typically at
+install time the driver will only register one available /dev/dsp device
+for its use. The 'dsps_order' module parameter allows for more devices
+to be allocated, as a power of two. Up to 4 devices can be registered
+( dsps_order=2 ). These devices act as fully distinct units and use
+separate channels in the maestro.
+As of version 0.14, this driver has a minimal understanding of PCI
+Power Management. If it finds a valid power management capability
+on the PCI device it will attempt to use the power management
+functions of the maestro. It will only do this on Maestro 2Es and
+only on machines that are known to function well. You can
+force the use of power management by setting the 'use_pm' module
+option to 1, or can disable it entirely by setting it to 0.
+When using power management, the driver does a few things
+differently. It will keep the chip in a lower power mode
+when the module is inserted but /dev/dsp is not open. This
+allows the mixer to function but turns off the clocks
+on other parts of the chip. When /dev/dsp is opened the chip
+is brought into full power mode, and brought back down
+when it is closed. It also powers down the chip entirely
+when the module is removed or the machine is shutdown. This
+can have nonobvious consequences. CD audio may not work
+after a power managing driver is removed. Also, software that
+doesn't understand power management may not be able to talk
+to the powered down chip until the machine goes through a hard
+reboot to bring it back.
+.. more details ..
+drivers/sound/maestro.c contains comments that hopefully explain
+the maestro implementation.