[Xenomai-help] Xenomai IRQ question

[Xenomai-help] Xenomai IRQ question

[Terry Fryar]

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Using xenomai irq's in user mode on a beaglexm.  It appears that irq latency
is around 44 microseconds from the edge until the isr is executed.  Is there
any way to reduce the latency?  Already using 99 as the priority for the isr
task.
 
Thanks!
 

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Re: [Xenomai-help] Xenomai IRQ question

[Gilles Chanteperdrix]

On 01/17/2012 12:36 AM, Terry Fryar wrote:
> Using xenomai irq's in user mode on a beaglexm.  It appears that irq latency
> is around 44 microseconds from the edge until the isr is executed.  Is there
> any way to reduce the latency?  Already using 99 as the priority for the isr
> task.

Handle the irq in kernel mode using an RTDM driver.

-- 
                                                                Gilles.

Re: [Xenomai-help] Xenomai IRQ question

[Terry Fryar]

Ok, on a falling edge irq, I'm using an RTDM driver and I'm down to 2.3uS,
which is quite an improvement.  However, it's still not fast enough...I need
to hit a window of about 500nS.  Any other suggestions?

I use the rtdm_irq_request to hook the ISR, and I set up the irq by hand
using mem mapping to directly access the registers on the beagle.  At this
point, I'm not sure where else to try and speed things up?

Thanks!


-----Original Message-----
From: Gilles Chanteperdrix [mailto:gilles.chanteperdrix@xenomai.org] 
Sent: Monday, January 16, 2012 6:24 PM
To: Terry Fryar
Cc: xenomai@xenomai.org
Subject: Re: [Xenomai-help] Xenomai IRQ question

On 01/17/2012 12:36 AM, Terry Fryar wrote:
> Using xenomai irq's in user mode on a beaglexm.  It appears that irq 
> latency is around 44 microseconds from the edge until the isr is 
> executed.  Is there any way to reduce the latency?  Already using 99 
> as the priority for the isr task.

Handle the irq in kernel mode using an RTDM driver.

-- 
                                                                Gilles.

Re: [Xenomai-help] Xenomai IRQ question

[Gilles Chanteperdrix]

On 01/17/2012 05:25 PM, Terry Fryar wrote:
> Ok, on a falling edge irq, I'm using an RTDM driver and I'm down to 2.3uS,
> which is quite an improvement.  However, it's still not fast enough...I need
> to hit a window of about 500nS.  Any other suggestions?

>From what I recall, irq latency under load on a 720 MHz OMAP3 is more
around 20us.

> 
> I use the rtdm_irq_request to hook the ISR, and I set up the irq by hand
> using mem mapping to directly access the registers on the beagle.  At this
> point, I'm not sure where else to try and speed things up?

500ns is not much. I do not think we support this kind of latency on any
processor.

-- 
                                                                Gilles.

Re: [Xenomai-help] Xenomai IRQ question

[Terry Fryar]

Ok, thanks Gilles!! 

-----Original Message-----
From: Gilles Chanteperdrix [mailto:gilles.chanteperdrix@xenomai.org] 
Sent: Tuesday, January 17, 2012 1:28 PM
To: Terry Fryar
Cc: xenomai@xenomai.org
Subject: Re: [Xenomai-help] Xenomai IRQ question

On 01/17/2012 05:25 PM, Terry Fryar wrote:
> Ok, on a falling edge irq, I'm using an RTDM driver and I'm down to 
> 2.3uS, which is quite an improvement.  However, it's still not fast 
> enough...I need to hit a window of about 500nS.  Any other suggestions?

>From what I recall, irq latency under load on a 720 MHz OMAP3 is more around
20us.

> 
> I use the rtdm_irq_request to hook the ISR, and I set up the irq by 
> hand using mem mapping to directly access the registers on the beagle.  
> At this point, I'm not sure where else to try and speed things up?

500ns is not much. I do not think we support this kind of latency on any
processor.

-- 
                                                                Gilles.