HAL user-land audio driver
HAL user-land audio driver
- Subject: HAL user-land audio driver
- From: "Mikael Hakman" <email@hidden>
- Date: Thu, 20 Mar 2008 14:44:58 +0100
- Organization: Datakonsulten AB
I've been experimenting with ways to implement HAL user-land audio driver,
including the example driver Jeff pointed me to. By inserting printf
statements in the code I can follow what happens during system boot in
console log. I can also see the same in a test application console. A
strange thing is, that the driver code accessed at system boot lags one
version behind the code that is accessed when using a test app.
I make a change to the driver code and build it. Then I move old driver from
/Library/Audio/PlugIns/HAL to the Trash, and copy the new version to that
directory. Then I reboot the system. In system console I can see that the
old version was still used during the boot. Then I run a test app, it
enlists available drivers using AudioHardware calls. In application's
console I can see that now the new version is used. If I then remove the new
driver from /Library/Audio/PlugIns/HAL and copy it again, then after a
reboot the new version is used by the system at boot time. It looks as if
the system cached the old code somewhere and used it at boot time. I can see
what version is used because the first thing my driver does, in its factory
function, is to printf its version number which I increment for each build.
Is there any way to get rid of this lagging?
Another issue, which I write here for informative purpose only, is the
following. If there is a segmentation violation in the driver code used at
boot time then OS X will not start at all. This is a little surprising
because this is user-land driver, not IOKit driver. At boot I get the usual
grey screen, then the light blue screen but login panel never appears. A
blank light blue screen is shown without any other thing happening. I have
to turn off and boot in single user mode and remove the faulty plug-in from
/Library/Audio/PlugIns/HAL. Then the system is able to boot normally again.
TIA
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