[ECOS] Re: Possible deadlock in SPI driver for AT91 ARM target

[ECOS] Re: Possible deadlock in SPI driver for AT91 ARM target

[Jonathan Larmour]

Svend Meyland Nicolaisen wrote:
> Hello
> 
> I am looking at the source, spi_at91.c, of the SPI driver for the AT91 ARM
> processor. In the function spi_at91_transfer the following code can be
> found:
> 
> =====>
>         cyg_drv_mutex_lock(&spi_bus->transfer_mx);
>         {
>             spi_bus->transfer_end = false;
>     
>             // Unmask the SPI int
>             cyg_drv_interrupt_unmask(spi_bus->interrupt_number);
>         
>             // Wait for its completition
>             cyg_drv_dsr_lock();
>             {
>                 while (!spi_bus->transfer_end)
>                     cyg_drv_cond_wait(&spi_bus->transfer_cond);
>             }
>             cyg_drv_dsr_unlock();
>         }    
>         cyg_drv_mutex_unlock(&spi_bus->transfer_mx);
> <=====
> 
> The transfer_cond condition is signalled in the DSR routine. Now if the
> DSR's are locked, how can the DSR routine be called to signal the condition?
> Am I missing something?

Yes ;-).

If a thread goes to sleep, the DSRs get unlocked again. When the thread
becomes runnable and is rescheduled, DSRs are relocked. You could consider
this to mean that the scheduler lock is a per-thread property.

Jifl
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RE: [ECOS] Re: Possible deadlock in SPI driver for AT91 ARM target

[Svend Meyland Nicolaisen]

 

> -----Original Message-----
> From: ecos-discuss-owner@ecos.sourceware.org 
> [mailto:ecos-discuss-owner@ecos.sourceware.org] On Behalf Of 
> Jonathan Larmour
> Sent: 3. marts 2008 16:46
> To: Svend Meyland Nicolaisen
> Cc: ecos-discuss@ecos.sourceware.org
> Subject: [ECOS] Re: Possible deadlock in SPI driver for AT91 
> ARM target
> 
> Svend Meyland Nicolaisen wrote:
> > Hello
> > 
> > I am looking at the source, spi_at91.c, of the SPI driver 
> for the AT91 
> > ARM processor. In the function spi_at91_transfer the following code 
> > can be
> > found:
> > 
> > =====>
> >         cyg_drv_mutex_lock(&spi_bus->transfer_mx);
> >         {
> >             spi_bus->transfer_end = false;
> >     
> >             // Unmask the SPI int
> >             cyg_drv_interrupt_unmask(spi_bus->interrupt_number);
> >         
> >             // Wait for its completition
> >             cyg_drv_dsr_lock();
> >             {
> >                 while (!spi_bus->transfer_end)
> >                     cyg_drv_cond_wait(&spi_bus->transfer_cond);
> >             }
> >             cyg_drv_dsr_unlock();
> >         }    
> >         cyg_drv_mutex_unlock(&spi_bus->transfer_mx);
> > <=====
> > 
> > The transfer_cond condition is signalled in the DSR routine. Now if 
> > the DSR's are locked, how can the DSR routine be called to 
> signal the condition?
> > Am I missing something?
> 
> Yes ;-).
> 
> If a thread goes to sleep, the DSRs get unlocked again. When 
> the thread becomes runnable and is rescheduled, DSRs are 
> relocked. You could consider this to mean that the scheduler 
> lock is a per-thread property.
> 

Ahh, thank you for your answer. Might be a good point to add to the
documentation..... :-)

/Svend


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Re: [ECOS] Re: Possible deadlock in SPI driver for AT91 ARM target

[Rob Duncan]

On 3/4/08, Svend Meyland Nicolaisen <ecos@smn.dk> wrote:
>  > If a thread goes to sleep, the DSRs get unlocked again. When
>  > the thread becomes runnable and is rescheduled, DSRs are
>  > relocked. You could consider this to mean that the scheduler
>  > lock is a per-thread property.
>  >
>
>  Ahh, thank you for your answer. Might be a good point to add to the
>  documentation..... :-)

I was confused by this to begin with as well.  It is actually in the
documentation but it's a bit easy to overlook.  Look at the
description of cyg_drv_cond_wait() in the Driver API section of the
Reference Manual.

Rob.

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