Timer Interrupt Handler

Adam Lackorzynski adam at os.inf.tu-dresden.de
Sun Jul 20 23:14:34 CEST 2014


On Fri Jul 18, 2014 at 11:27:16 +0200, Xavier LEBARS wrote:
> > -----Message d'origine-----
> > De : l4-hackers [mailto:l4-hackers-bounces at os.inf.tu-dresden.de] De la part
> > de Adam Lackorzynski
> > Envoyé : jeudi 17 juillet 2014 23:21
> > À : l4-hackers at os.inf.tu-dresden.de
> > Objet : Re: Timer Interrupt Handler
> > Importance : Haute
> > 
> > On Wed Jul 16, 2014 at 15:10:29 +0200, Xavier LEBARS wrote:
> > > I'm always trying to configure the timer for my Zedboard and the
> > > system clock doesn't advance. I checked this in the
> > > Timer::system_clock() function
> > >
> > >
> > >
> > > In order to construct my timer driver, I use mptimer option, so I
> > > configured the private timer of my board in the file
> > > timer-arm-mptimer.cpp. Private Timers call the function interval()
> > > which use the global timer of the board  (bsp/zynq/
> > > timer-arm-mptimer-zynq.cpp
> > > file) Here is a part of the implementation of my global timer (I just
> > > launch counter) :
> > >   Mmio_register_block
> > t(Kmem::mmio_remap(Mem_layout::Gpt_phys_base));
> > >   t.write<Mword>(0, GPT_CR);
> > >
> > >   t.write<Mword>(0, GPT_CNT0);
> > >
> > >   t.write<Mword>(0, GPT_CNT1);
> > >   t.modify<Mword>(GPT_CR_EN, 0, GPT_CR);
> > >   Mword vc = start_as_counter();
> > >
> > >   while (t.read<Mword>(GPT_CNT0) < Gpt_ticks)
> > >     ;
> > >   Mword interval = (vc - stop_counter()) / Ticks;
> > >
> > >   t.write<Mword>(0, GPT_CR);
> > >
> > >   return interval;
> > 
> > Is this calculating a proper interval value? For a start you can also just return a
> > fixed value.
> 
> With  this configuration :   
>  Timer_freq = 32768,
>  Ticks = 50,
> 
> I obtain the following interval value : 85899345

That's far too large.

> When I try to use a fixed value like in Tegra configuration (249 999
> or 499 999), I see no effects.

Values must be in this range given the frequency the system uses.

> > > The private timers are bind to the GIC with the IRQ 27, so I mentioned
> > > this value in the static unsigned irq() function.
> > 
> > Why 27 and not 29?
> 
> A mistake between  Global Timer Interrupts ID 27 and private timer interrupts ID 29

Ok.

> > > Panic - Could not allocate scheduling IRQ 27
> > >
> > > The origin of this problem is the allocate_irq() function
> > >
> > > So do I have to modify something in my IRQ manager or did I forget one
> > > step during the construction of my timer driver ? Thanks in advance
> > 
> > For the mptimer it should just work given a proper interval() value.
> > So does the mptimer tick, i.e. reading the counter register multiple times
> > gives a changing value everytime? Regarding the interrupt number, timer-
> > arm-mptimer.cpp already has it defined.
> 
> The counter register value change correctly

It also wraps around? So there's no IRQ29. Does the UART IRQ work, i.e.
entering JDB via ESC works (saying 'IRQ ENTRY')?



Adam
-- 
Adam                 adam at os.inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/



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