Re: [PATCH] Fix infinite loop in grub_pit_wait()

[Christian Franke <Christian.Franke@t-online.de>]

Robert Millan wrote:
> On Thu, Aug 07, 2008 at 05:32:42PM +0200, Christian Franke wrote:
>   
>> grub2 from current SVN hangs if run in VirtualPC, the problem was 
>> introduced with 'svn diff -r 1779:1780'.
>>     
>
> I'm not familiar with this part of the PIT interface;  why does it hang
> only on VirtualPC?
>
>   

Possibly different BIOS init of 0x61? Or different implementation of the 
legacy hardware, which IIRC looks like this:

.                 +-------+     /--------->0x61[5]
.    ...--Clock-->| Timer |     |
.0x61[0]---Gate-->|   2   |-Out-+->+---+
.                 +-------+        | & |-->Speaker
.0x61[1]-------------------------->+---+


Resulting values of "tsc_ticks_per_ms" (AMD 3.2@2Ghz):

.           orig    with patch
VMware:     ~1500    ~2000000
VirtualBox: ~2000000 ~2000000
VirtualPC:  hang     ~2000000


>> ...
>> +  /* Disable timer2 gate and speaker.  */
>> +  grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE), TIMER2_REG_LATCH);
>>  }
>>     
>
> This doesn't AFAICT preserve the existing value of the timer2 gate and speaker.
> I assume that is ok?
>
>   

IMO yes. The timer state itself cannot be preserved, so it should be 
safe to leave it disabled. To test, try If BIOS speaker output (echo -e 
"\a") still works.


> Thanks!
>
>   

You're welcome.

Patch committed.

Christian