Thread safe updating variables

[JoYa_4140271]

In ARM CortexM architecture, is it interrupt safe (atomic) to update uint16_t, uint32_t variables?

I'm guessing that __disable_irq() does return previous interrupt status, is that correct? Thank you.

[LinglingG_46 · Accepted solution]

if you use "__disable_irq()", it will close the interrupt, but it will wait the interrupt handler to finish run, then return.

But if you use "disable_irq_nosync", it will return to the previous status.

It is safe to update the uint16_t, uint32_t variables.

[NoriTan]

If you are using PSoC Creator, Following context can be used.

void xx_isr(void) {
    uint32_t status = Cy_SysLib_EnterCriticalSection();
    count++;
    Cy_SysLib_ExitCriticalSection(status);
}

The function Cy_SysLib_EnterCriticalSection() disables interrupts and returns previous status.

The function Cy_SysLib_ExitCriticalSection() returns to the previous state using the saved status.

It is effective for non-atomic value like uint64_t

  17:main_cm4.c    ****     uint32_t status = Cy_SysLib_EnterCriticalSection();
  38 0002 FFF7FEFF              bl      Cy_SysLib_EnterCriticalSection
  39                    .LVL0:
  18:main_cm4.c    ****     count++;
  41 0006 0549                  ldr     r1, .L3
  42 0008 D1E90023              ldrd    r2, [r1]
  43 000c 0132                  adds    r2, r2, #1
  44 000e 43F10003              adc     r3, r3, #0
  45 0012 C1E90023              strd    r2, [r1]
  19:main_cm4.c    ****     Cy_SysLib_ExitCriticalSection(status);
  47 0016 FFF7FEFF              bl      Cy_SysLib_ExitCriticalSection

Regards,

Noriaki