Re: [Qemu-devel] [PATCH] TSC2005 interrupt handling fix

[Riihimaki Juha (Nokia-D-MSW/Helsinki)]

On Jan 8, 2009, at 09:27, ext andrzej zaborowski wrote:

> > For issue #1 specifically, when this happens with the current  
> > version, all
> > DAV bits for the running conversion function are set by the timer  
> > tick
> > callback even if some of the results had already been read out and  
> > the
> > corresponding DAV bits cleared. Now, when the guest ISR is finished  
> > and it
> > clears the IRQ, some DAV bits in the TSC2005 will remain set and  
> > this leads
> > to the TSC2005 never to raise a new interrupt again (at least with  
> > function
> > 1 in use).
>
> The ISR doesn't clear the IRQ -- it can only clear the irq mask flag.
> If the TSC2005 still keeps the IRQ pin high, then the cpu should
> immediately jump to the ISR again.

True; in the scenario I used for testing PINTDAV is programmed as DAV  
(CFR2 bit 14 is set) and thus the ISR tries to deassert the interrupt  
condition at the TSC2005 by reading all conversion results. It is of  
course the TSC2005 itself that needs to actually clear the interrupt.  
However in the condition I described above, the ISR will not try to  
read new conversion results from the TSC2005 if the interrupt has not  
been cleared in between -- which will not happen if some of the DAV  
bits stay set. This is how it looks like from the TSC2005's viewpoint,  
I have not read the ISR code. Neither have I checked whether the  
problem is that the ISR is not executed at all or if it for some  
reason just refuses to talk with the TSC2005.

> We shouldn't be trying to change the tsc2005 emulation so that the
> driver works, we should change it so that it behaves as described in
> the specification from TI.  I think the real issue is that we start a
> new conversion before the irq is deasserted, i.e. the following check
> in tscXXXX_pin_update
>
>    if (!s->enabled || s->busy)
>        return;
>
> should become
>
>    if (!s->enabled || s->busy || s->dav)
>        return;
>
> or something similar.  It would be good to check on the real tsc2005
> when exactly the DAC becomes busy (bit 14 of CFR0) in the different
> modes.

My original change to overcame this was also a small change; I only  
changed the setting of the DAV bits in the timer callback function to  
set the bits only if the bits for the current function were all clear.  
That had similar effect to the change you are proposing here however  
issue #2 remains still. Perhaps it's just my eyes but I did not find  
any information on TI's spec on the exact timing of the interrupt  
line, for example the time between reading the last available data  
value and when the interrupt is cleared and how quickly after that the  
interrupt line can be raised again.


Regards,
Juha