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Forum: ARM programming with GCC/GNU tools understanding interrupts


Author: outer_space (Guest)
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I am trying to make systime.c work in mthomas' latest demo.  systime.c
is from the EFSL demo, simply adding systime.c to the makefile,
including the header, and calling systime_init does not work.  What
happens is that the chip is reset every millisecond for about 3 seconds
and then it hangs up completely.

Is this the instruction that points to the FIQ function?  What is going
on here?  Address of the FIQ function loads here?
ldr         r0 , [r8, #AIC_FVR]

Here is a section from the startup assembly file. (where above
instruction came from)


        .section   .reset
        .text
        .global _startup
        .func   _startup
_startup:
reset:
/*---------------------------------------------------------------------- 
--------
//*- Exception vectors
//*--------------------
//*- These vectors can be read at address 0 or at RAM address
//*- They ABSOLUTELY requires to be in relative addresssing mode in
order to
//*- guarantee a valid jump. For the moment, all are just looping.
//*- If an exception occurs before remap, this would result in an
infinite loop.
//*- To ensure if a exeption occurs before start application to infinite
loop.
//*--------------------------------------------------------------------- 
---------*/

                B           InitReset           /* 0x00 Reset handler */
undefvec:
                B           undefvec            /* 0x04 Undefined
Instruction */
swivec:
                B           swivec              /* 0x08 Software
Interrupt */
pabtvec:
                B           pabtvec             /* 0x0C Prefetch Abort
*/
dabtvec:
                B           dabtvec             /* 0x10 Data Abort */
rsvdvec:
                B           rsvdvec             /* 0x14 reserved  */
irqvec:
                B           IRQ_Handler_Entry   /* 0x18 IRQ   */
fiqvec:                                   /* 0x1c FIQ  */
/*---------------------------------------------------------------------- 
--------
//*- Function             : FIQ_Handler_Entry
//*- Treatments           : FIQ Controller Interrupt Handler.
//*- Called Functions     : AIC_FVR[interrupt]
//*--------------------------------------------------------------------- 
---------*/

FIQ_Handler_Entry:

/*- Switch in SVC/User Mode to allow User Stack access for C code   */
/* because the FIQ is not yet acknowledged*/

/*- Save and r0 in FIQ_Register */
            mov         r9,r0
      ldr         r0 , [r8, #AIC_FVR]
            msr         CPSR_c,#I_BIT | F_BIT | ARM_MODE_SVC

/*- Save scratch/used registers and LR in User Stack */
            stmfd       sp!, { r1-r3, r12, lr}

/*- Branch to the routine pointed by the AIC_FVR */
            mov         r14, pc
            bx          r0

/*- Restore scratch/used registers and LR from User Stack */
            ldmia       sp!, { r1-r3, r12, lr}

/*- Leave Interrupts disabled and switch back in FIQ mode */
            msr         CPSR_c, #I_BIT | F_BIT | ARM_MODE_FIQ

/*- Restore the R0 ARM_MODE_SVC register */
            mov         r0,r9

/*- Restore the Program Counter using the LR_fiq directly in the PC */
            subs        pc,lr,#4
  .align 0
.RAM_TOP:
  .word  Top_Stack


Here is part of the .map file where FIQ_Handler_Entry doesnt show up,
but AT91F_Default_FIQ_handler does show up. (why?)

.text           0x00100000      0xe38
 *Cstartup.o(.text)
 .text          0x00100000      0x13c Cstartup.o
                0x001000bc                IRQ_Handler_Entry
                0x0010010c                AT91F_Default_FIQ_handler
                0x00100000                _startup
                0x00100110                AT91F_Default_IRQ_handler
                0x00100114                AT91F_Spurious_handler
                0x001000b8                exit

Then I went to this part of the assembly file

        .global AT91F_Default_FIQ_handler
        .func   AT91F_Default_FIQ_handler
AT91F_Default_FIQ_handler:
            b     AT91F_Default_FIQ_handler
        .size   AT91F_Default_FIQ_handler, . - AT91F_Default_FIQ_handler
        .endfunc

I modified "b     AT91F_Default_FIQ_handler" to "b     systime_isr"
Which is obviously the wrong thing to do because it lead me to where I
am at right now.

Thanks for help.
-Outer_space

Author: Martin Thomas (Guest)
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outer_space wrote:
> I am trying to make systime.c work in mthomas' latest demo.  systime.c
> is from the EFSL demo, simply adding systime.c to the makefile,
> including the header, and calling systime_init does not work.  What
> happens is that the chip is reset every millisecond for about 3 seconds
> and then it hangs up completely.

Sorry, but I provide a lot of example-code. Do you mean the
AT91SAM-"gamma" example?

The gamma-Example uses a different "approach" for handling exceptions
than the AT91-efsl-Demo. In the "gamma"-Example there is a
Assembler-Wrapper which is called when an INT-Exception occures. The
AT91-example directly uses the Vector-Address of the AIC to branch to
the ISR and in the ISR are helper-macros. This is not compatible either
use a "wrapper/no macros" or no "wrapper/direct call and the macros".

I have created an new EFLS-package which will be available soon. The
AT91SAM example in the package is based on the "gamma"-Code and includes
a modified "systime.c". Please check
http://www.siwawi.arubi.uni-kl.de/avr_projects/arm...
today evening (GMT).

> Is this the instruction that points to the FIQ function?  What is going
> on here?  Address of the FIQ function loads here?
> ldr         r0 , [r8, #AIC_FVR]

It seems you confuse the FIQ-Handler with the INT-Handler.

> Here is a section from the startup assembly file. (where above
> instruction came from)
> [skip]
>I modified "b     AT91F_Default_FIQ_handler" to "b     systime_isr"
>Which is obviously the wrong thing to do because it lead me to where I
>am at right now.

Yes. As far is I remember the systime-Interrupt is configured as INT not
FIQ.

Mabye useful part from the new efsl-example (based on the
AT91-"gamma"-example). Keep startup-code as is in gamma and replace the
ISR in systime.c with:

/*__ramfunc*/ void systime_isr(void)         /* System Interrupt Handler
*/
{
  volatile unsigned long status;
  static int cnt;

  // Interrupt Acknowledge
  status = AT91C_BASE_PITC->PITC_PIVR;

  systime_value++;                       /* Increment Time Tick */

  cnt++;
  if (cnt >= 500) {     /* 500ms Elapsed ? */
    *AT91C_PIOA_ODSR ^= LED2;          /* Toggle LED2 */
    cnt=0;
  }
}

Hope this helps,
Martin Thomas

Author: outer_space (Guest)
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> Hope this helps,
> Martin Thomas


Fantastic.

-outer_space

Author: Narasimha Rao (snrao)
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Hi Martin,

I would like to know how to assign a timer interrupt for 50ms with
AT91SAM7s64 / AT91SAM9261 MCU.

Please send me if you have some info regarding this. I am using IAR
EWARM version

Regards
Narasimha Rao

my ID is snrao007@yahoo.com

outer_space wrote:
>
>> Hope this helps,
>> Martin Thomas
>
>
> Fantastic.
>
> -outer_space

Author: Martin Thomas (Guest)
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Narasimha Rao wrote:
> I would like to know how to assign a timer interrupt for 50ms with
> AT91SAM7s64 / AT91SAM9261 MCU.

When using the SAM7S PIT see describtion of Register PIMR. Sorry, but
the datasheet describes the needed setup better than I could here in a
few words.

Author: Narasimharao (Guest)
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Martin Thomas wrote:
> Narasimha Rao wrote:
>> I would like to know how to assign a timer interrupt for 50ms with
>> AT91SAM7s64 / AT91SAM9261 MCU.
>
> When using the SAM7S PIT see describtion of Register PIMR. Sorry, but
> the datasheet describes the needed setup better than I could here in a
> few words.


Hi Martin,

Thank you for the reply.

I am unable to configure the FIQ interrupt for AT91SAM7s64.

I followed the steps as per the datasheet like Configuring the
peripherals
Configure interrupt
Enable Interrupt
And issuing Software trigger.

Still the FIQ was not invoking. What could be the reason??

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