stm32f4 wakeup interrupt

[Christian Mauderer]

Am 29.04.19 um 03:36 schrieb Jython:
> Thank you a lot ! maybe i was thinking make code more clear and then
> forget the right

No problem. Pointer bugs are most likely one of the most common ones for
C programmers. You know the 4 most common bugs:

- wrong parentheses
- pointer bugs
- off by one errors

Note: No real statistic behind that. But I liked the joke when I first
read it ;-)

Best regards

Christian

> 
> On Sun, Apr 28, 2019 at 3:27 PM Christian Mauderer <list at c-mauderer.de
> <mailto:list at c-mauderer.de>> wrote:
> 
>     Am 27.04.19 um 16:40 schrieb Christian Mauderer:
>     > Am 24.04.19 um 10:00 schrieb Jython:
>     >> HI, ALL!
>     >> why the code stuck in wakeup handler while the RTC gets time work
>     fine
>     >> i have checked some days, but no register error found, i suspect that
>     >> the handler function is the issue
>     >>
>     >>
>     >> // code
>     >> rtems_isr rtc_wakeup_handler(rtems_vector_number vector)
>     >> {
>     >>    
>     >>     uint32_t STM32F4_RTC_ISR = (*(volatile uint32_t *)(0x4000280C));
>     >>    
>     >>     // clear 10bit
>     >>     if(STM32F4_RTC_ISR & (1<<10))
>     >>     {
>     >>         //printk("wak\n");
>     >>         STM32F4_RTC_ISR &= ~(1<<10);
>     >>         STM32F4_RTC_ISR &= 0xfffffbff;
>     >>     }
>     >>    
>     >>     volatile uint32_t EXIT_PR = *(volatile uint32_t*)0x40013C14;
>     >>     printk("before clr %08x\n", EXIT_PR);
>     >>     EXIT_PR |= 1<<22;
>     >>    
>     >>     int i;
>     >>     for(i = 0; i < 1000; i++) i = i + 1 - 1;
>     >>     printk(" %08x\n", EXIT_PR);
>     >> }
>     >>
>     >>
>     >> the printed log attached,  why the EXIT_PR bit22 not cleared
>     >>
>     >>
>     >
>     > Hello Jython,
>     >
>     > your EXIT_PR seems to be slightly odd. What you do:
>     >
>     >     volatile uint32_t EXIT_PR = *(volatile uint32_t*)0x40013C14;
>     >
>     > This means you read the content of 0x40013C14 and write it to a 32 bit
>     > value.
>     >
>     > Later you do
>     >
>     >     EXIT_PR |= 1<<22;
>     >
>     > This changes the _copy_ of the value.
>     >
>     > What you most likely want to do is the following:
>     >
>     >     volatile uint32_t *EXIT_PR = (volatile uint32_t*)0x40013C14;
>     >     *EXIT_PR |= 1<<22;
>     >
>     > This would change the value at 0x40013C14 and not only your copy.
>     >
>     > By the way: You tried to do a busy wait. That's not a good idea in an
>     > interrupt. The way you implemented it, the compiler most likely even
>     > just removes it:
>     >
>     >     int i;
>     >     for(i = 0; i < 1000; i++) i = i + 1 - 1;
>     >
>     > The compiler most likely notices that this statement has no effect. If
>     > you would like to implement a busy wait that way, you should use a
>     > volatile int.
>     >
>     > Note that RTEMS has a rtems_counter_delay_nanoseconds() function. That
>     > is a busy wait loop. It is based on the CPU counter and provides a
>     > method for short busy waits for example during driver initialization.
>     > But again: Please don't use busy waits in Interrupts. It's not a good
>     > idea and will lead to problems sooner or later.
>     >
>     > Best regards
>     >
>     > Christian Mauderer
> 
>     Oh, and I just noted: You are writing a one to the register but expect
>     the bit to be cleared. So it is most likely a "write one to clear"
>     register (which is quite common for interrupt flags). In that case you
>     maybe don't want to use a
> 
>         *EXIT_PR |= 1<<22;
> 
>     but a
> 
>         *EXIT_PR = 1<<22;
> 
>     Otherwise you clear other flags in that register too. Please have a look
>     at the reference manual of your chip to decide that.
> 
>     Best regards
> 
>     Christian
>