Re: [Mactel-linux-users] Turning off the obnouxious power-on sound

[Sam N. <sa...@th...>]

On Sat, 2009-08-29 at 04:02 +0200, Alexandre Boeglin wrote:
> Hi, the variable you are looking for is named "SystemAudioVolume".
> When
> the sound is muted in OS X System properties, it is equal to 0x80, so
> I
> guess the most significant bit is a flag. Otherwise, the value seems
> to
> represent a percentage, taking values between 0x03 up to 0x64 (but the
> scale is not linear, as 25% in System properties is represented by
> 0x32).
> 
> Or at least this is how it seems to work on my 2006 Mac Pro.
> 
> To modify this in the EFI shell, it seems that you have to use the
> dmpstore command, saving the variable to a file, modifying the file,
> then loading it back.

Hey! that works fine. Thanks very much Alex.

For posterity the process on my non-pro2,1 goes something like this:

#<Boot EFI shell>
#<spend 30 minutes finding the page break switch for help :) >
Shell>help -b

#<cd to a writable partition (I had booted from a refit CD, so fs0 was
the disk, fs1 was the 100MB efi partition)>
Shell>fs1:
fs1:\>

#<dump the nvram variable>
fs1:\>dmpstore SystemAudioVolume -s sav.txt

#<edit the the dumped variable with a hexeditor (probably wiser to keep
the original dump and edit a copy)>
fs1:\>hexedit save.txt


#<load the new nvram variable>
fs1:\>dmpstore SystemAudioVolume -l sav.txt

#<exit to refit and reboot>
fs1:\>exit

Enjoy the BONGless restart.

So for a while it wasn't apparent what value to change with the
hexeditor, and tbh, not being familiar with any hexeditor, I'm not sure
I got it right. Further experimentation indicates I may have just borked
it, but apparently that also serves to make it shut up.

The files (now back in Debian) look like this:

$ cat SystemAudioVolume.txt
$SystemAudioVolumeaC|*��K���A�\��
q  <-with no newline


$ hexdump -C SystemAudioVolume.txt
00000000  24 00 00 00 53 00 79 00  73 00 74 00 65 00 6d 00  |$...S.y.s.t.e.m.|
00000010  41 00 75 00 64 00 69 00  6f 00 56 00 6f 00 6c 00  |A.u.d.i.o.V.o.l.|
00000020  75 00 6d 00 65 00 00 00  10 61 43 7c 2a ab bb 4b  |u.m.e....aC|*..K|
00000030  a8 80 fe 41 99 5c 9f 82  07 00 00 00 01 00 00 00  |...A.\..........|
00000040  71                                                |q|
00000041

(In hexedit.efi the 00000041 line did not appear.)

Since running dmpstore SystemAudioValume by itself returned output
something like:
00000: 71 "q"
I took a guess and replaced the 71 with Alex's 80 getting:

$ hexdump -C SystemAudioVolume80.txt 
00000000  24 00 00 00 53 00 79 00  73 00 74 00 65 00 6d 00  |$...S.y.s.t.e.m.|
00000010  41 00 75 00 64 00 69 00  6f 00 56 00 6f 00 6c 00  |A.u.d.i.o.V.o.l.|
00000020  75 00 6d 00 65 00 00 00  10 61 43 7c 2a ab bb 4b  |u.m.e....aC|*..K|
00000030  a8 80 fe 41 99 5c 9f 82  07 00 00 00 01 00 00 00  |...A.\..........|
00000040  80                                                |.|
00000041

Which turned off the bong and I'm happy. But for kicks I also tried 32
(for 25% more BONG)

$ hexdump -C sav.txt 
00000000  24 00 00 00 53 00 79 00  73 00 74 00 65 00 6d 00  |$...S.y.s.t.e.m.|
00000010  41 00 75 00 64 00 69 00  6f 00 56 00 6f 00 6c 00  |A.u.d.i.o.V.o.l.|
00000020  75 00 6d 00 65 00 00 00  10 61 43 7c 2a ab bb 4b  |u.m.e....aC|*..K|
00000030  a8 80 fe 41 99 5c 9f 82  07 00 00 00 01 00 00 00  |...A.\..........|
00000040  32                                                |2|
00000041

But that also gave me silence, so I think I'm doing it 'wrong.'
However reloading the original (71) file did bring back the bonging. So
I don't think any of this is particularly dangerous for those who may
want to here the noise again someday. :)