We now only reset the PCM out channel during initialization, and handle
the case where the channel's current index has passed the last valid
index properly.
This fixes issues with stuttering audio between multiple subsequent
`aplay` invocations, for example.
This might help with debugging on bare metal. Since the minimum version
that can be specified is revision 2.1, and we do not use any feature
from revision 2.2 or newer, this is merely future-proofing ourselves
for new features yet to be built. Additionally, removing the `VERIFY()`
ensures we will not crash on cards that only support earlier revisions.
The Qemu AC'97 device stops its PCM channel's DMA engine when it is
running and the sample rate is changed. We now make sure the DMA engine
is restarted after changing the sample rate, allowing you to e.g. run
`asctl set r 22050` during `aplay` playback.
This driver is not tested and probably not used on any modern hardware
machine, because it is plugged into the ISA bus and not the PCI bus.
Also, the run script doesn't utilize this device anymore, making it more
hard to test this driver and to ensure it doesn't rot.
The SB16 card driver doesn't swallow more than 4096 bytes of data at
once, so instead of asserting just return ENOSPC for now.
To test this, either play normal sound or just this (very!) loud noise:
dd if=/dev/random of=/dev/audio/0 bs=4096
We have 3 new components:
1. The AudioManagement singleton. This class like in other subsystems,
is responsible to find hardware audio controllers and keep a reference
to them.
2. AudioController class - this class is the parent class for hardware
controllers like the Sound Blaster 16 or Intel 82801AA (AC97). For now,
this class has simple interface for getting and controlling sample rate
of audio channels, as well a write interface for specific audio channel
but not reading from it. One AudioController object might have multiple
AudioChannel "child" objects to hold with reference counting.
3. AudioChannel class - this is based on the CharacterDevice class, and
represents hardware PCM audio channel. It facilitates an ioctl interface
which should be consistent across all supported hardware currently.
It has a weak reference to a parent AudioController, and when trying to
write to a channel, it redirects the data to the parent AudioController.
Each audio channel device should be added into a new directory under the
/dev filesystem called "audio".
This was broken in commit 0a1b34c753 / PR #11687 since the buffer
descriptor list size was not page-aligned, and the new
`MM.allocate_dma_buffer_pages` expects a page-aligned size.
The fixes are:
1. Don't copy PCI::DeviceIdentifier during construction. This is a heavy
structure to copy so we definitely don't want to do that. Instead, use
a const reference to it like what happens in other parts in the Kernel.
2. Declare the constructor as explicit to avoid construction errors.
Previously we `VERIFY()`ed that the device supports variable-rate audio
(VRA). Now, we query the VRA bit and if VRA is not supported, we do not
enable double-rate audio and disallow setting any sample rate except
the fixed 48kHz rate as defined by the AC'97 specification. This should
allow the driver to function on a wider array of hardware.
Note that in the AC'97 specification, DRA without VRA is allowed when
supported: this effectively doubles the sample rate to 96kHZ. For now,
we ignore that possibility and let it default to 48kHZ.
Executing `asctl set r 96000` no longer results in weird sample rates
being set on the audio devices. SB16 checks for a sample rate between 1
and 44100 Hz, while AC97 implements double-rate support which allows
sample rates between 8kHz and 96kHZ.
This factors out some hardcoded PCMOut registers into a new private
class called AC97Channel, which wraps around a channel's registers and
provides some shared functionality.
No functional changes.
