Chris Breitenbach wrote:
> Hello all,
>
> I’m currently setting up my AT91SAM7S256 (Olimex EvalBoard, Yagarto
> Toolchain) and try to implement interrupts in RAM-code, however I don’t
> succeed. I have checked all available sample code (from various forums,
> from Martin Thomas, etc.) and – at least to me – the code looks OK, but
> still no satisfying result..
>
> My project is based on Jim Lynch’s tutorial, I use (without
> modification) blinker.c, crt.s, isrsupport.c, lowlevelinit.c,
> script.ocd, makefile, demo_at91sam7_blink_ram.cmd, and all h- and
> a-files.
> Main.c looks like this:
>
> //  *******************************************************
> #include "AT91SAM7S256.h"
> #include "board.h"
> #include "math.h"
> #include "stdlib.h"
> #include "string.h"
>
> //                External References
> extern  void LowLevelInit(void);
> //extern  unsigned enableIRQ(void);  //xxx
> //extern  unsigned enableFIQ(void);  //xxx
> AT91PS_PIO p_PIO;
> AT91PS_PMC p_PMC;
> AT91PS_AIC p_AIC;
>
> unsigned int  FiqCount = 0;    // global uninitialized variable
>
> //interrupt handler: switch off LED1
> void interrupt_handler_button (void)
> {
>   p_PIO->PIO_SODR = LED1;    //switch off LED1
> }
>
> int  main (void) {
>
>   unsigned int test;
>   unsigned long k;
>
>   p_PIO = AT91C_BASE_PIOA;
>   p_PMC = AT91C_BASE_PMC;
>   p_AIC = AT91C_BASE_AIC;
>
>   LowLevelInit();
>
>   p_PMC->PMC_PCER = (1 << AT91C_ID_PIOA);
> //  p_PMC->PMC_PCER = (1<<AT91C_ID_IRQ0);             //yyy
> //  p_PMC->PMC_PCER = (1<<AT91C_ID_IRQ1);             //yyy
>   test=p_PMC->PMC_PCSR;
>
>   p_PIO->PIO_PER = LED_MASK;  //activate I/O for LEDs
>   p_PIO->PIO_OER = LED_MASK;  //configure LEDs as ouput
>   p_PIO->PIO_CODR = LED1 | LED2;  //define initial status of output pins
>   p_PIO->PIO_SODR = LED3;    //define initial status of output pins
>   p_PIO->PIO_PER = SW_MASK;  //activate I/O for buttons
>   p_PIO->PIO_ODR = SW_MASK;  //configure buttons #1, #2 as input
>   p_PIO->PIO_IFER = SW_MASK;  //activate glitch filtering
>   p_PIO->PIO_MDDR = SW_MASK;  //deactivate multi drive control
>   p_PIO->PIO_PPUER = SW_MASK;  //activate pull-ups for buttons
>
>   p_AIC->AIC_IDCR = 0x1<<AT91C_ID_PIOA;  //firstly, deactivate interrupt
>   p_AIC->AIC_SVR[AT91C_ID_PIOA] = (unsigned int)
> interrupt_handler_button;  //specify interrupt handler function
>   p_AIC->AIC_SMR[AT91C_ID_PIOA] =
> (AT91C_AIC_SRCTYPE_POSITIVE_EDGE|AT91C_AIC_PRIOR_HIGHEST);  //interrupt
> typ+priority
>   p_AIC->AIC_ICCR = 0x1<<AT91C_ID_PIOA;  //read (and clear) interrupts
>   p_PIO->PIO_IER = SW_MASK; //activate input change interrupt of buttons
>   p_AIC->AIC_IECR = AT91C_ID_PIOA;  //enable interrupts
>
>   //enable interrupts
> //  enableIRQ();                //xxx
> //  enableFIQ();                //xxx
>
>   while (1) {
>     //blink LED1
>     if  ((p_PIO->PIO_ODSR & LED2) == LED2)
>       p_PIO->PIO_CODR = LED2;    // LED1 (DS1) on
>     else
>       p_PIO->PIO_SODR = LED2;    // LED1 (DS1) off
>
>     for (k = 1000000; k != 0; k-- );  // wait 1 second
>
>   }
> }
>
>
> My most urgent question is, why does the interrupt not work? I would
> expect that the function interrupt_handler_button is entered when I
> press one of the push-buttons, but nothing happens!
>
> Other open questions are:
> - when I un-comment the code lines marked with yyy, I would expect to
> read in the variable “test” the result of having activated AT91C_ID_IRQ0
> and AT91C_ID_IRQ1. But that’s not the case, PMC_PCSR’s bit 30 and 31 can
> never be set to 1. Why?
> - Do I need Jim’s code lines marked with xxx (enableIRQ and enableFIQ)
> or can I drop them if I write my own interrupt handlers (e.g. functions
> like interrupt_handler_button)? I have a feeling that I should always
> use at least enableIRQ to be able to use nested interrupt handlers, but
> I’d like to confirm this assumption.
>
> Thanks a lot for any answer,
>
> christian

Hi Christian,

The type of interrupt that you want is definitely an IRQ interrupt, so
you probably want call the enableIRQ in your program. The reason that
your interrupts are not working might have something to do with your
startup code. It is not shown here, so I am just guessing, but....

I would first check in what processor mode your code runs. The startup
code initializes the various stacks and specifies whether or not the
IRQ's and FIQ's are enabled for all processor modes. Suppose that the
startup code switches to USR mode and disables the IRQ's (Sets the
I-bit), then it is not so easy to enable it in your C-program. Since the
ARM processor does not allow you do clear the IRQ flag while in USR
mode, the enableIRQ function does not work. Switching to another mode
while in USR mode is not easy either.

So, either you have to change your startup code and keep running in SYS
mode, or you have to write a SWI handler and write some SWI code that
does enable the interrupts. When the swi instruction is executed, the
processor mode switches to SVC mode, and then you can clear the IRQ flag
for USR mode.

But then again, I am just guessing since I do not know what your startup
code does.

Kees.