Re: [Xenomai-core] [BUG] x86 TSC emulation broken

[Jan Kiszka <jan.kiszka@domain.hid>]

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Philippe Gerum wrote:
> On Sun, 2006-07-23 at 19:28 +0200, Jan Kiszka wrote:
>> Hi,
>>
>> I happened to switch on some CPU type that enabled the Xenomai's TSC
>> emulation code. The result was an ugly lock-up: endless loop in the
>> timer IRQ handler.
>>
>> The reason: the TSC emulation collides with the VT sound output / the PC
>> speaker driver. Over 2.6, one can easily avoid this my switching off
>> CONFIG_INPUT_PCSPKR. 2.4 requires to export and than manipulate
>> kb_mksound (the pointer to the sound gen*
>> erating code).
> 
> There is an issue in the Adeos 2.4 patch (1.2-05) which is not
> preventing the kernel from poking into the 8254 registers to determine
> the current time offset.

But the TSC emulation itself is not an Adeos service. Shouldn't it be
better moved? Then I would happily leave it up to you. :)

> 
>> The latter pointer rang some bell. I once fixed a broken RTAI build due
>> to that code. So I pulled out vulcano and actually found the related
>> code + an extension of the original ipipe patch to export kb_mksound. I
>> guess it would have been too complicated for Paolo to explain the reason
>> of this export to us...
>>
>> Anyway, this digging revealed another potential breakage in the
>> emulation code: RTAI takes care to read the emulated TSC at least once
>> per 50 ms, to avoid overflows I assume. Xenomai does not.
> 
> Mm, through the host timer service, it should at least each 10ms period.

Yeah, true. I probably got blinded by the existing RTAI code. There is
just the likely theoretical case that there is no host tick (LAPIC +
emulated TSC? Not configurable, is it?).

Jan


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