[U-Boot-Users] Bogus External Interrupt

[U-Boot-Users] Bogus External Interrupt

[do]

Hello,

I am trying to write simple program similar to examples/timer.c, which 
uses interrupts from general purpose timers.

My board is based on mpc8260 and I am using U-boot 1.1.4.

When interrupt is generated from timer, there also appears message: 
Bogus External Interrupt IRQ 0.

I don't know why bogus interrupt appears and how it is related to my 
timer interrupt.This is also strange that the number of IRQ is 0. This 
bogus interrupt appears only when timer is started. When I have 
registered my timer interrupt handler with irq_install_handler, but not 
started timer, everything was ok, and I was able to check with irqinfo 
that my handler is registered.

I would be grateful for some suggestions what can be wrong.

Best regards!

[U-Boot-Users] Bogus External Interrupt

[Jerry Van Baren]

do wrote:
> Hello,
> 
> I am trying to write simple program similar to examples/timer.c, which 
> uses interrupts from general purpose timers.
> 
> My board is based on mpc8260 and I am using U-boot 1.1.4.
> 
> When interrupt is generated from timer, there also appears message: 
> Bogus External Interrupt IRQ 0.
> 
> I don't know why bogus interrupt appears and how it is related to my 
> timer interrupt.This is also strange that the number of IRQ is 0. This 
> bogus interrupt appears only when timer is started. When I have 
> registered my timer interrupt handler with irq_install_handler, but not 
> started timer, everything was ok, and I was able to check with irqinfo 
> that my handler is registered.
> 
> I would be grateful for some suggestions what can be wrong.
> 
> Best regards!

Typically "IRQ 0" is an indication that there was no interrupt found 
when the ISR went to read the interrupt reason.  I can think of two 
reasons for this:
1) (Typical reason): an interrupt happened and was withdrawn (level 
sensitive interrupt: it went inactive) before the processor got to the ISR.

2) (Likely your problem): The ISR cleared the interrupt improperly so 
that the processor (re)latched the interrupt that was cleared.  When you 
exit the ISR, the processor has a pending interrupt so it re-enters the 
ISR, but doesn't find anything to do.  Typically this is caused by 
clearing the processor side of the interrupt and _then_ clearing the 
source.  You should clear the source _first_ and then the processor (or, 
for a multi-level interrupt, clear from the furthest out inward).

This should be a non-fatal error, but should be understood and fixed.

gvb

[U-Boot-Users] Re: Bogus External Interrupt

[do]

Jerry Van Baren napisa?(a):

> 2) (Likely your problem): The ISR cleared the interrupt improperly so 
> that the processor (re)latched the interrupt that was cleared.  When you 
> exit the ISR, the processor has a pending interrupt so it re-enters the 
> ISR, but doesn't find anything to do.  Typically this is caused by 
> clearing the processor side of the interrupt and _then_ clearing the 
> source.  You should clear the source _first_ and then the processor (or, 
> for a multi-level interrupt, clear from the furthest out inward).
> 
> This should be a non-fatal error, but should be understood and fixed.
> 

I think that the procesor relatched the interrupt that was cleared by 
the m8260_mask_and_ack(irq) procedure in external_interrupt servicing 
function. Thank you for your suggestions.
One of the solutions can be splitting this procedure in two, for 
example: m8260_mask_irq(irq) and m8260_ack_irq(irq). The first can be 
used for masking interrupt before ISR (mask register usage), and second 
for ack after ISR (pending interrupt register usage), when the reason of 
interrupt is cleared. There can be also enabled other interrupts for 
multi-level.

Best regards!


PS. I hope that the following patch (although not perfect) can be 
helpful for others:


diff -uNr u-boot-org/cpu/mpc8260/interrupts.c 
u-boot/cpu/mpc8260/interrupts.c
--- u-boot-org/cpu/mpc8260/interrupts.c	2006-01-25 23:13:34.000000000 +0100
+++ u-boot/cpu/mpc8260/interrupts.c	2006-03-06 11:35:53.000000000 +0100
@@ -92,6 +92,20 @@
  	simr[word] = ppc_cached_irq_mask[word];
  }

+static void m8260_ack_irq (unsigned int irq_nr)
+{
+	volatile immap_t *immr = (immap_t *) CFG_IMMR;
+	int bit, word;
+	volatile uint *sipnr;
+
+	bit = irq_to_siubit[irq_nr];
+	word = irq_to_siureg[irq_nr];
+
+	sipnr = &(immr->im_intctl.ic_sipnrh);
+	sipnr[word] = 1 << (31 - bit);
+}
+
+
  static void m8260_unmask_irq (unsigned int irq_nr)
  {
  	volatile immap_t *immr = (immap_t *) CFG_IMMR;
@@ -180,10 +194,8 @@

  	irq = m8260_get_irq (regs);

-	m8260_mask_and_ack (irq);
-
-	enable_interrupts ();
-
+	m8260_mask_irq(irq); /* enable_interrupts(); */ /* for multi-level*/
+	
  	if (irq_handlers[irq].handler != NULL)
  		(*irq_handlers[irq].handler) (irq_handlers[irq].arg);
  	else {
@@ -194,7 +206,11 @@
  		 */
  		unmask = 0;
  	}
-
+	
+	m8260_ack_irq(irq);
+	
+	
  	if (unmask)
  		m8260_unmask_irq (irq);
  }