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Author
Varuzhan Danielyan
Posted
1-Feb-2005 06:17
Toolset
ARM
New! Global Interruption Disable/Enable
Which is the easiest way for Global Interruptions Disable/Enable in CA for LPC2129?

Varuzhan
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Author
Keil Reinhard
Posted
1-Feb-2005 07:05
Toolset
ARM
New! RE: Global Interruption Disable/Enable
There are really two solutions to this problem.

1. If you need just a single routine that has the interrupt system disabled, you should write a __swi function. swi (= software interrupt) prevents that a function can be interrupted by an __irq. __fiq functions are not blocked.

2. For specific interrupt blocking see:
http://www.keil.com/support/docs/2888.htm

Reinhard
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Author
Varuzhan Danielyan
Posted
1-Feb-2005 12:01
Toolset
ARM
New! RE: Global Interruption Disable/Enable
As I understand, if program uses both IRQ and FIQ, the __swi function cannot be used. More, if I want to disable interruptions not for the whole function, but only for a part of code, I must write to the VICIntEnClr register as in the example. But in the example one need to disable only TIMER0 interruption. What if I need to disable all interruptions?
If I write

temp = VICIntEnable;
VICIntEnClr = temp;
...
VICIntEnable = temp;

there is a risk, that if interruption happened between the two first operators, and the interrupt handler changes the value of the VICIntEnable register, a wrong value will be restored by the last operator.
Am I wrong?
Is there an absolutely reliable way to disable ALL interruptions for LPC2100? It is so easy in other microcontrollers.

Varuzhan
Read-Only
Author
Keil Reinhard
Posted
1-Feb-2005 12:05
Toolset
ARM
New! RE: Global Interruption Disable/Enable
You are correct about the __swi, but why do you need to block an fiq?

It would be dangerous to change VICIntEnable in an interrupt function! You should not partice this programming style.

Reinhard
Read-Only
Author
Varuzhan Danielyan
Posted
1-Feb-2005 12:06
Toolset
ARM
New! RE: Global Interruption Disable/Enable
As I understand, if program uses both IRQ and FIQ, the __swi function cannot be used. More, if I want to disable interruptions not for the whole function, but only for a part of code, I must write to the VICIntEnClr register as in the example. But in the example one need to disable only TIMER0 interruption. What if I need to disable all interruptions?
If I write

temp = VICIntEnable;
VICIntEnClr = temp;
...
VICIntEnable = temp;

there is a risk, that if interruption happened between the two first operators, and the interrupt handler changes the value of the VICIntEnable register, a wrong value will be restored by the last operator.
Am I wrong?
Is there an absolutely reliable way to disable ALL interruptions for LPC2100? It is so easy in other microcontrollers.

Varuzhan
Read-Only
Author
Varuzhan Danielyan
Posted
1-Feb-2005 12:13
Toolset
ARM
New! RE: Global Interruption Disable/Enable
I am sorry for repeating message - bad working telephone line.
I agree about the bad stile.
Then can I define two macros:

unsigned int temp;
#define _DISABLE (temp = VICIntEnable; VICIntEnClr = temp);

#define _ENABLE (VICIntEnable = temp;)

and use them in my code?

Thank you,
Varuzhan
Read-Only
Author
Varuzhan Danielyan
Posted
1-Feb-2005 12:21
Toolset
ARM
New! RE: Global Interruption Disable/Enable
Sure, without brackets
Read-Only
Author
Keil Reinhard
Posted
2-Feb-2005 01:00
Toolset
ARM
New! RE: Global Interruption Disable/Enable
Each ARM controller is somehow different.

A generic solution to disable all interrupts is to set the CPSR I + F flag (similar code as documented under: http://www.keil.com/support/docs/2910.htm).

But tell my: why can you not use the __swi method?

Reinhard
Read-Only
Author
Varuzhan Danielyan
Posted
2-Feb-2005 02:04
Toolset
ARM
New! RE: Global Interruption Disable/Enable
Thank you very much!
The __swi method is really nice, but sometimes one will not want to have a function call overhead to protect only a couple of instructions.

Another question: do the methods, mentioned in whole this topik, including the __swi, protect from Spurious Interrupts?

Varuzhan
Read-Only
Author
Jon Ward
Posted
2-Feb-2005 09:03
Toolset
ARM
New! RE: Global Interruption Disable/Enable
The __swi method is really nice, but sometimes one will not want to have a function call overhead to protect only a couple of instructions.

Isn't the __swi call less code (and overhead) than disabling interrupts?

do the methods, mentioned in whole this topik, including the __swi, protect from Spurious Interrupts?

Masking interrupts inhibits interrupts (spurious or not). However, a spurious interrupt is an unexpected interrupt. Once interrupts are unmasked, the spurious interrupt triggers. Then, the interrupt handler will need to handle it.

Jon

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