You as a programmer should consider what bugs may be introduced by an interrupt triggering at an inopportune time. Write_csr(mie, read_csr(mie) | (1 << 7)) Ĭare should be taken when developing safety- or timing-critical applications with interrupts as they are asynchronous events and can be triggered at any time during program execution. Reset_timer(MTIME_CLK_FREQ / (2 * BLINK_FREQ)) timer_handler() function at index 7 of the array. #ACTIVE TIMER IN AFTER EFFECTS CODE#The machine timer interrupt is exception code 7 as shown in so we put the #define BLINK_FREQ 4 // This is an arbitrary constant used to specify the LED blink frequency In a multiprocessor system, the PLIC routes the peripheral interrupt to an appropriate processor to handle it. The FE310 also has a platform-level interrupt controller (PLIC) that collects interrupts from other peripherals. #ACTIVE TIMER IN AFTER EFFECTS SOFTWARE#Software interrupts are used for interprocessor communication and debugging. The FE310 has a core-local interruptor (CLINT) that handles timer and software interrupts. Interrupts are the hardware exceptions discussed in Section 6.6.2. After handling the interrupt, the processor then returns to the user program and seamlessly continues where it was interrupted. When an event occurs, the microcontroller stops the executing program and jumps to an interrupt handler that responds to the interrupt. Most microcontrollers support interrupts. This can be a waste of the processor’s power and makes it difficult to write programs that do interesting work while simultaneously waiting for events to occur. So far, we have relied on polling, in which the program continually checks a value until an event occurs such as data arriving on a UART or a timer reaching its compare value. Harris, David Harris, in Digital Design and Computer Architecture, 2022 9.3.8 Interrupts Under typical network conditions, τ hovers close to the maximum but, on occasions when the oscillator frequency wanders more than about 1 ppm, τ quickly drops to lower values until the wander subsides. In the opposite case holds for some number of updates, τ is increased. If | θ| exceeds this sum, the oscillator frequency is deviating too fast for the clock discipline to follow, so τ is reduced. The sum of the peer dispersion and select dispersion is used as a measure of oscillator instability in both the PLL and FLL modes. The time constant is not used when the FLL is in use. At τ = 64s, this results in a 90% time response of about 900 s and a 63% frequency response of about 3600 s, which is a useful compromise under most operating conditions. When the PLL is in use, the time constant is directly proportional to τ. While in the PLL α < 1 is necessary for stability, its affect on dynamics when the FLL is in use is minor.Ī key feature of the NTP design is the selection of τ in response to measured local clock stability. A secondary reason is to reduce the effects of phase noise, since in the NTP model the local clock of one stratum can be used to discipline clocks at the next higher stratum. The primary reason is to avoid discontinuities when the offset x k is very large, e.g., over 100 ms. It may seem strange that the coefficient a in (6) is used in both the FLL and PLL modes. The NTP clock discipline uses the adjtime() mechanism to control the VFO and implements the impulse response F( t) using the algorithm described below. The adjtime() system call is used to select one of the three frequencies and how long δt to run, in order to amortize the specified offset. The oscillator can actually run at three different frequencies, one at the intrinsic oscillator frequency, a second slightly higher and a third slightly lower. When tick does not evenly divide 1 s (1 000 000 μs), an additional increment fixtick is added to time once each second to make up the difference. The value of tick is chosen so that time, once properly initialized, is equal to the present time of day in seconds and microseconds relative to a given epoch. Each interrupt causes an increment tick to be added to the kernel time variable. The Unix 4.3bsd timekeeping functions are implemented using a hardware timer interrupt produced by an oscillator in the 100-1000 Hz range. Mills, in Readings in Multimedia Computing and Networking, 2002 VII.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |