Hi, Does anyone know if the enable_irq / disable_irq functions take care of nested calls or do I have to do this manually? That is, if enable_irq is called twice, do the interrupts re-enable after 1 or 2 calls of disable_irq? The ARM Compiler Reference Guide (http://www.keil.com/support/man/docs/armccref/armccref_CJAFBCBB.htm) suggests it needs to be done manually, assuming these are the same functions. Might be useful info to add to the Working with Interrupts Handbook (http://mbed.org/handbook/Working-with-Interrupts).

#include <mbed.h>

void EnableIRQTwice()
{
    __enable_irq();
    __enable_irq();
}

void DisableIRQTwice()
{
    __disable_irq();
    __disable_irq();
}

int main() 
{
    printf("EnableIRQTwice():  %X\n", (unsigned int)EnableIRQTwice & ~1);
    printf("DisableIRQTwice(): %X\n", (unsigned int)DisableIRQTwice & ~1);
    
    printf("Done\n");
    for(;;)
    {
    }
}

EnableIRQTwice():  1AC
DisableIRQTwice(): 1B0
Done

rearm ~/Downloads/IRQTest_LPC1768.bin --start 0x1AC --size 8
EnableIRQTwice:
000001AC  B662       CPSIE i
000001AE  4770       BX LR
DisableIRQTwice:
000001B0  B672       CPSID i
000001B2  4770       BX LR

I think you have to take care of it manually as the reference you cited indicates. I tried out the following piece of code with the online compiler: <<code>> #include <mbed.h> void EnableIRQTwice() { __enable_irq(); __enable_irq(); } void DisableIRQTwice() { __disable_irq(); __disable_irq(); } int main() { printf("EnableIRQTwice(): %X\n", (unsigned int)EnableIRQTwice & ~1); printf("DisableIRQTwice(): %X\n", (unsigned int)DisableIRQTwice & ~1); printf("Done\n"); for(;;) { } } <</code>> This code generated the following output showing the addresses of the function which use these intrinsics: <<code>> EnableIRQTwice(): 1AC DisableIRQTwice(): 1B0 Done <</code>> When I disassembled the functions at these addresses, I see: <<code>> rearm ~/Downloads/IRQTest_LPC1768.bin --start 0x1AC --size 8 EnableIRQTwice: 000001AC B662 CPSIE i 000001AE 4770 BX LR DisableIRQTwice: 000001B0 B672 CPSID i 000001B2 4770 BX LR <</code>> This output shows two things of interest. * These irq related compiler intrinsics just resolve down to the corresponding CPSIE and CPSID assembler instructions. There is no nesting level check. * The optimizer in the compiler was even smart enough to remove the redundant call to these IRQ related compiler intrinsics. Hope that helps, Adam