clock | 易学教程

Solving Metastability Using Double-Register Approach

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For solving metastability caused by different clock domains in Verilog, double-register method is used. But as far as I know, the final output of metastability is undetermined. Output is independent of input. So, my question is how to guarantee the correctness of output using double-register method? Thanks. You cannot be completely sure that you avoided metastability. As you mentioned, the output of a metastable flip-flop is unpredictable so you can potentially propagate a wrong value when you have metastability even with the 'two-register' approach. This method however never intended to solve

How to measure function running time in Qt?

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I am calling argon2 - memory intensive hashing function in Qt and measuring its running time: ... QTime start = QTime::currentTime(); // call hashing function QTime finish = QTime::currentTime(); time = start.msecsTo(finish) / 1000.0; ... In argon2 library's test case, time is measured in another way: ... clock_t start = clock(); // call hashing function clock_t finish = clock(); time = ((double)finish - start) / CLOCKS_PER_SEC; ... I am calling the function exactly as they call in their test case. But I am getting a twice bigger number (twice slower). Why? How to measure function running time

Multiple cell phone alarms, which one covers the other. Which alarm is preceded? How it works?

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Lets say i set up two alarms 09:00:00 (alarm1) 09:10:00 (alarm2) and every alarm can snooze for 10 minutes. Then alarm1 sounds and i snooze it at 09:00:10 so it must ring again at 09:10:10 BUT at time 09:10:00 already the alarm2 is ringing an i snooze it at 09:10:11. what will happen to the alarm1? when will the first alarm be replayed? To me the following happened. When it was time for the alarm2 to be activated, the alarm1 actually activated. 1st experiment: I postponed alarm1 and the alarm2 deactivated. 2nd experiment: I turned the alarm1 off and the alarm2 was activate, but it was

react native show current time and update the seconds in real-time

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问题 I want to show the current time(MM/DD/YY hh:mm:ss) in react native app like a clock, and get update every seconds, I tried using new Date() and set it in state, but the time don't update unless I refresh the page. I also tried using setInterval function in render(), it do got update but it's expensive for CPU. is there a good method to realise the function? state = { curTime: null, } render(){ setInterval(function(){this.setState({curTime: new Date().toLocaleString()});}.bind(this), 1000);

Concept of clock tick and clock cycles

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I have written a very small code to measure the time taken by my multiplication algorithm : clock_t begin, end; float time_spent; begin = clock(); a = b*c; end = clock(); time_spent = (float)(end - begin)/CLOCKS_PER_SEC; I am working with mingw under Windows. I am guessing that end = clock() will give me the clock ticks at that particular moment. Subtracting it from begin will give me clock ticks consumed by multiplication. When I divide with CLOCKS_PER_SEC , I will get the total amount of time. My first question is: Is there a difference between clock ticks and clock cycle? My algorithm here

Emulator's clock doesn't match the host system clock

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问题 Why doesn't the Android emulator's clock match the host system clock? It's not a time zone difference --it's always off by several minutes. Is there a way to synchronize them besides manually setting the emulator's time? 回答1: I believe there is no way to synchronize the time. The default image of the emulator sets to UTC/GMT (+00:00). However you can change it to your own. Here is an image on how to do so: First un-check the "Automatic Time Zone" (red arrow) then click on the "Selected Time

Is the use of rising_edge on non-clock signal bad practice? Are there alternatives?

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I am working on a VHDL design and I have it working, but the code is pretty ugly and the fact that it seems that I am trying to work around the language's design to accomplish my goal makes me feel like something is wrong. I'm pretty new to VHDL, but I have been working on smaller chunks of the project for nearly a month so I have the general idea. However, This part is a bit more complex. I need a process that will create a one clock period long pulse (LOAD_PULSE) after the rising edge of a signal (END_ADC), but not until 4 clocks has passed from the latest rising edge of that signal (END_ADC

Object angle based on current time

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问题 Listen carefully, because this is specific. I'm trying to make an analog clock in iPhone SDK. I've been trying to accomplish this for three weeks now, I've asked five questions on SO, and I still have found almost NOTHING. I need help. I want to have a clock hand that simply rotates depending on the current time. I'm mostly focused on the second hand right now because it seems like the easiest. I don't necessarily care what is used to rotate the clock hand (CALayers, UIView, etc.), just as

How to make pthread_cond_timedwait() robust against system clock manipulations?

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问题 Consider the following source code, which is fully POSIX compliant: #include <stdio.h> #include <limits.h> #include <stdint.h> #include <stdlib.h> #include <pthread.h> #include <sys/time.h> int main (int argc, char ** argv) { pthread_cond_t c; pthread_mutex_t m; char printTime[UCHAR_MAX]; pthread_mutex_init(&m, NULL); pthread_cond_init(&c, NULL); for (;;) { struct tm * tm; struct timeval tv; struct timespec ts; gettimeofday(&tv, NULL); printf("sleep (%ld)\n", (long)tv.tv_sec); sleep(3); tm =

How to have loop sync with UTC timer and execute at every new minute?

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I want to have a loop be executed once every minute when datetime.utcnow().second is zero. So far I have this while True: while datetime.utcnow().second != 0: pass do_something() But the problem with this is that I am wasting cpu processes. I would use time.sleep(60) , but I don't know how it would sync with the UTC clock, because time.sleep(60) could stray from the official UTC time as time passes. Best way I can think of would be to sleep until the next minute: while True: sleeptime = 60 - datetime.utcnow().second time.sleep(sleeptime) ... If you want to be really precise: while True: t =