Differences between interrupt service routine (ISR) and a subroutine

Hi

What are the differences between ISR and a subroutine in embedded
systems, how about the following:
- interrupts are disabled by the microprocessor prior to calling the
isr
- isr's are always smaller
- an isr cannot be written in C
- a subroutine always has arguments
- the CPU flags are stored on the stack in addition to the return
address

Thanks

"2005" <uws2003@yahoo.com> wrote in message 
news:1164736936.337323.40270@j44g2000cwa.googlegroups.com...
> Hi

This is another homework question isn't it?

> What are the differences between ISR and a subroutine in embedded
> systems, how about the following:
> - interrupts are disabled by the microprocessor prior to calling the
> isr

Not always - google for nested interrupts.

> - isr's are always smaller

Not necessarily. ISRs _should_ be kept small but that doesn't always 
happen.

> - an isr cannot be written in C

Not true but when written in C you normally need an attribute to tell 
the compiler that the function is to be an ISR.

> - a subroutine always has arguments

Not true. void Subroutine(void); is a perfectly acceptable prototype.

> - the CPU flags are stored on the stack in addition to the return
> address

That is true (although I suspect some pedants will find an example of 
systems that don't).

In article <1164736936.337323.40270@j44g2000cwa.googlegroups.com>, 
uws2003@yahoo.com says...
> Hi
> 
> What are the differences between ISR and a subroutine in embedded
> systems, how about the following:
> - interrupts are disabled by the microprocessor prior to calling the
> isr
Not always true.
> - isr's are always smaller
not true
> - an isr cannot be written in C
definitely just wrong
> - a subroutine always has arguments
nope
> - the CPU flags are stored on the stack in addition to the return
> address
Depends on the CPU
> 
> Thanks
No problem

Thanks and wondering if
- difference between an isr and a subroutine is that an isr has no
arguments
is true or not?

In article <1164739817.612931.190780@l39g2000cwd.googlegroups.com>, 
uws2003@yahoo.com says...
> 
> Thanks and wondering if
> - difference between an isr and a subroutine is that an isr has no
> arguments
> is true or not?
> 
Since you don't know what is in the resisters when the ISR is jumped to 
the idea of function arguments is meaningless.

Tom Lucas wrote:

> > - the CPU flags are stored on the stack in addition to the return
> > address
>
> That is true (although I suspect some pedants will find an example of
> systems that don't).

:)

The ARM CPU copies the return address and the CPU flags into special
registers. If you need reentrant interrupts, you need to copy them to
the stack yourself.

"James Beck" <jim@reallykillersystems.com> wrote in message 
news:MPG.1fd6562aaec84d6d989d8e@newsgroups.bellsouth.net...
> In article <1164739817.612931.190780@l39g2000cwd.googlegroups.com>,
> uws2003@yahoo.com says...
>>
>> Thanks and wondering if
>> - difference between an isr and a subroutine is that an isr has no
>> arguments
>> is true or not?
>>
> Since you don't know what is in the resisters when the ISR is jumped to
> the idea of function arguments is meaningless.

Well I can see some good uses for interrupts with arguments,
making interrupt routines even easier to write in C. I'm sure
someone has patented the idea already as it is quite obvious...

Wilco 

On 2006-11-28, Wilco Dijkstra <Wilco_dot_Dijkstra@ntlworld.com> wrote:

>> Since you don't know what is in the resisters when the ISR is
>> jumped to the idea of function arguments is meaningless.

The unstated assumption seems to be that function arguments are
passed in registers?

> Well I can see some good uses for interrupts with arguments,
> making interrupt routines even easier to write in C. I'm sure
> someone has patented the idea already as it is quite obvious...

Obvious but impossible (in general). The hardware designer has
no way of knowing how the ISR is going to expect arguments to
be passed. If varies from one language to the next, from one
compiler to the next, and even from one build to the next when
compiler flags are changed.

-- 
Grant Edwards                   grante             Yow!  My life is a patio
                                  at               of fun!
                               visi.com            

On 28 Nov, in article
     <1164736936.337323.40270@j44g2000cwa.googlegroups.com>
     uws2003@yahoo.com "2005" wrote:
>Hi
>
>What are the differences between ISR and a subroutine in embedded
>systems, how about the following:

Sounds like a homework question, you want somebody else to answer
for you.

Hint see if you can find a difference between interupts and functions
on NON embedded systems.

>- interrupts are disabled by the microprocessor prior to calling the
>isr
>- isr's are always smaller
>- an isr cannot be written in C
>- a subroutine always has arguments
>- the CPU flags are stored on the stack in addition to the return
>address

Well I suggest you go back and read the book again, as these appear
to be badly copied from a text book.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.gnuh8.org.uk/>              GNU H8 & mailing list info
<http://www.badweb.org.uk/>             For those web sites you hate

2005 <uws2003@yahoo.com> wrote:
> Hi
> 
> What are the differences between ISR and a subroutine in embedded

Stick it up your ass, cheat.

pete
-- 
pete@fenelon.com "he just stuck to buying beer and pointing at other stuff"