6/28/2023 0 Comments Cdock source![]() The local APIC timer sends interrupts only to its processor, while the PIT raises a global interrupt, which may be handled by any CPU in the system.The APIC’s timer counter is 32 bit long, while the PIT’s timer counter is 16 bit long.The Local APIC (Advanced Programmable Interrupt Controller) present in recent 80x86 microprocessors provide yet another time measuring device, and it is a device, similar to the PIT, which can issue one-shot or periodic interrupts. Linux may take advantage of this register to get much more accurate time measurements. When using this register the kernel has to take into consideration the frequency of the clock signal: if, for instance, the clock ticks at 1 GHz, the TSC is increased once every nanosecond. Starting with the Pentium, 80x86 microprocessors sport a counter that is increased at each clock signal and is accessible through the TSC register which can be read by means of the rdtsc assembly instruction. Time Stamp Counter (TSC)Īll 80x86 microprocessors include a CLK input pin, which receives the clock signal of an external oscillator. As time goes by, the PIT goes on issuing interrupts forever at some fixed (architecture-specific) frequency established by the kernel. Instead of ringing a bell, the PIT issues a special interrupt called timer interrupt, which notifies the kernel that one more time interval has elapsed. The PIT is a time-measuring device that can be compared to the alarm clock of a microwave oven: it makes the user aware that the cooking time interval has elapsed. Linux uses the RTC only to derive the time and date at boot time. The RTC is capable of issuing interrupts at frequencies ranging between 2 Hz and 8,192 Hz. ![]() As it is energized by a small battery, it continues to tick even when the system is switched off. The RTC is independent of the system’s CPU and any other chips. Let’s briefly describe the clock and timer circuits that are usually found with any nearly modern system of those architectures: Real Time Clock (RTC) For instance, IA-32 and AMD64 systems have at least one programmable interrupt timer (PIT) as a classical timer circuit, which is usually implemented by an 8254 CMOS chip. The timer circuits are programmed by the kernel, so they issue interrupts at a fixed, and predefined, frequency. The clock circuits are used both to keep track of the current time of the day and to make precise time measurements. So, which hardware is available depends on the particular architecture. Every typical system has several devices, usually implemented by clock chips, that provide timing features and can serve as clocks. When it comes to talking about a system’s clock, the hardware sits at the very bottom. Thank you again for all that you do - for your school and for your community.An overview on hardware clock and system timer circuits ![]() And we’d love to feature you on Texas Football Today - our daily live show every weekday at noon on /Live! We’re proud to be owned and operated in the Lone Star State!īefore the season kicks off, we look forward to seeing you at the 2020 Texas High School Coaches Convention in San Antonio, where you can pick up a FREE COPY of Dave Campbell’s Texas Football at our large exhibit area. Dave Campbell’s Texas Football is excited to kick off another season providing coaches, players and fans with the best, most complete football preview in the state! Please fill out the accompanying Texas Football 2020 Coaches Questionnaire so that we’ll have the information we need to continue providing complete coverage of your team for the fans in your community and around the state.
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