LPC1768 EXT0 interrupt huge lag

navman <naveen_pn@n_o_s_p_a_m.yahoo.com> wrote:
> Is there any workaround/ideas to circumvent this lag? I feel cheated by the
> Cortex-M3 spec which claims "12 cycles interrupt latency".         

In addition to placing the ISR in RAM, check the peripheral clocks.

-a

- Placed the ISR in RAM (and verified it is in RAM in the map file)
- Remapped interrupt vector to RAM
- Ensured that the peripheral clock speed is same as core clock.

Still getting about 400ns lag from the falling edge to toggling of IO pin
inside the interrupt. Can't figure out how to get the "12 cycles" lag as
advertised for Cortex M3. Any more ideas? 	   
					
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On 7/6/2011 10:49 AM, navman wrote:
> - Placed the ISR in RAM (and verified it is in RAM in the map file)
> - Remapped interrupt vector to RAM
> - Ensured that the peripheral clock speed is same as core clock.
>
> Still getting about 400ns lag from the falling edge to toggling of IO pin
> inside the interrupt. Can't figure out how to get the "12 cycles" lag as
> advertised for Cortex M3. Any more ideas? 	
> 					
> ---------------------------------------		
> Posted through http://www.EmbeddedRelated.com

Have you tried talking to your NXP FAE?

-- 
Rob Gaddi, Highland Technology
Email address is currently out of order

Op Thu, 23 Jun 2011 19:50:41 +0200 schreef navman  
<naveen_pn@n_o_s_p_a_m.yahoo.com>:
> Hi,
> I've setup LPC1768 for external falling edge interrupt on EINT0 pin and  
> in the interrupt handler, I just clear the interrupt flag and make a pin
> (P0.0) low and immediately high again. When I check the EINT0 pin and the
> output pin P0.0 on an oscilloscope, there is a huge lag, about 520ns
> between the falling edge of EINT0 & the P0.0 becoming low.

The external interrupts each have a glitch filter.  This could be a large  
portion of your "lag".



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>The external interrupts each have a glitch filter.  This could be a large 

>portion of your "lag".

The glitch filters add just 5ns lag according to the datasheet. 

>Have you tried talking to your NXP FAE?

I've contacted NXP and awaiting their response. 

	   
					
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On Thu, 07 Jul 2011 22:32:46 -0500, "navman"
<naveen_pn@n_o_s_p_a_m.yahoo.com> wrote:

>>The external interrupts each have a glitch filter.  This could be a large 
>
>>portion of your "lag".
>
>The glitch filters add just 5ns lag according to the datasheet. 
>
>>Have you tried talking to your NXP FAE?
>
>I've contacted NXP and awaiting their response. 

FWIW, I tried the external interrupt experiment on an STM32 CM3 with
similar (500-ish ns) results. Architectural issue?

-- 
Rich Webb     Norfolk, VA