Your understanding is pretty close; the trick is that most compilers will never write system calls, because the functions that programs call (e.g. getpid(2), chdir(2), etc.) are actually provided by the standard C library. The standard C library contains the code for the system call, whether it is called via INT 0x80 or SYSENTER. It’d … Read more
It may not help in your situation (since it doesn’t work in the simulator), but activating Siri works in a similar way to a phone call, sending your application to the background and interrupting audio, so is easier to test than making a call. Siri is on iPhone 4S and above, iPod touch 5th gen, … Read more
If the event of interest is: Asynchronous Urgent Infrequent then an interrupt based handler would make sense. If the event of interest is: Synchronous (i.e. you know when to expect it within a small window) Not Urgent (i.e. a slow polling interval has no ill effects) Frequent (i.e. majority of your polling cycles create a … Read more
Interrupts can be viewed as a mean of communication between the CPU and the OS kernel. Signals can be viewed as a mean of communication between the OS kernel and OS processes. Interrupts may be initiated by the CPU (exceptions – e.g.: divide by zero, page fault), devices (hardware interrupts – e.g: input available), or … Read more
A gate (call, interrupt, task or trap) is used to transfer control of execution across segments. Privilege level checking is done differently depending on the type of destination and instruction used. A call gate uses the CALL and JMP instructions. Call gates transfer control from lower privilege code to higher privilege code. The gate DPL … Read more
ARM calls FIQ the fast interrupt, with the implication that IRQ is normal priority. In any real system, there will be many more sources of interrupts than just two devices and there will therefore be some external hardware interrupt controller which allows masking, prioritization etc. of these multiple sources and which drives the interrupt request … Read more