[Haskell-cafe] Re: Computer time, independent of date
patients, I wanted to be sure not to save wrong information. It wouldn't matter if the clock is saying we are on XVII century, as long as 10 seconds would never be 10.1. What are the interval durations you need to measure? Since they are from equipment, what is the spec? I read from serial port. When the equipment was available for testing, we measured the output to be a few thowsand bytes/second. The program is supposed to run in Windows computers at physicians offices (and their only requirement is to be able to run windows and have a serial port). Errors of 1 byte per second would be acceptable, even if they accumulate. I have no equipment specs and, right now, no equipment to test. (Yes, I know this is crazy.) So, I need to know what kind of problems I may expect, so I'm able to deal with them. Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Steve Schafer ha scritto: On Fri, 09 Jan 2009 09:28:49 -0600, you wrote: I'm not sure that the original question implied *that* level of need. I can't imagine being worried about leap seconds yet at the same time being willing to accept the potential vagaries of any of the built-in clocks. POSIX realtime extensions have been developed to be high reliable. I don't know if the implementations on general purpose operating systems like Linux are reliable, but in case of problems one can try to switch to a real time operating system. This resources may be useful: http://juliusdavies.ca/posix_clocks/clock_realtime_linux_faq.html Timing is, however, a complex issue. Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
On Sat, 10 Jan 2009 15:04:36 +0100, you wrote: POSIX realtime extensions have been developed to be high reliable. I think people are missing the details here. Yes, the built-in real-time clocks have excellent long-term accuracy. They run UTC-based correction algorithms using NTP, and are thus traceable to TAI. However, they offer no guarantees on interval measurements, and the correction algorithms can cause the measurement of a time interval of an hour or so duration to be off by +/- 1 sec, especially within the first few hours after a cold boot. If you care about leap seconds, you should certainly care about that magnitude of error. Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Computer time, independent of date
POSIX realtime extensions have been developed to be high reliable. (...) However, they offer no guarantees on interval measurements, and the correction algorithms can cause the measurement of a time interval of an hour or so duration to be off by +/- 1 sec, especially within the first few hours after a cold boot. (...) At the start of this thread, my assumption was that all computers had a 100% reliable tick counter. Well, this shows I understand nothing about hardware. My problem is that the equipment I interact with is supposed to deliver data at a constant rate. Since I don't know how much its engineers care about patients, I wanted to be sure not to save wrong information. It wouldn't matter if the clock is saying we are on XVII century, as long as 10 seconds would never be 10.1. But, as I learned from you, my PC is not to be considered as a reference. Maybe the right approach is to ask people who understand hardware if mine is actually a valid concern. Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Mauricio ha scritto: POSIX realtime extensions have been developed to be high reliable. (...) However, they offer no guarantees on interval measurements, and the correction algorithms can cause the measurement of a time interval of an hour or so duration to be off by +/- 1 sec, especially within the first few hours after a cold boot. (...) At the start of this thread, my assumption was that all computers had a 100% reliable tick counter. High Precision Event Timer (http://en.wikipedia.org/wiki/HPET) should be pretty reliable, but it will never be as reliable as a dedicated clock. Well, this shows I understand nothing about hardware. My problem is that the equipment I interact with is supposed to deliver data at a constant rate. What is the rate value? How do you read the data? Since I don't know how much its engineers care about patients, I wanted to be sure not to save wrong information. You should trust the engineers, IMHO, since that is a medical equipment and should be more reliable than a PC. Read carefully the equipment specification. It wouldn't matter if the clock is saying we are on XVII century, as long as 10 seconds would never be 10.1. But, as I learned from you, my PC is not to be considered as a reference. Maybe the right approach is to ask people who understand hardware if mine is actually a valid concern. If you can, you should ask to the equipment producer. If you are on a POSIX system, store both the time information from the equiment and from clock_gettime(CLOCK_MONOTONIC), but only trust the equipment. Thanks, Maurício Regards Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Computer time, independent of date
Mauricio wrote: patients, I wanted to be sure not to save wrong information. It wouldn't matter if the clock is saying we are on XVII century, as long as 10 seconds would never be 10.1. Chris (yes I am an experimental physicist) asks: What are the interval durations you need to measure? 0.1 second is very different from 1 ms or 0.1 μs ! (1 ms is the atomic time radio signal accuracy) (0.1 μs can be had with GPS receivers) Since they are from equipment, what is the spec? What is the error tolerance for these durations? How are these errors allowed or forbidden to accumulate? Since you say you do not trust the incoming timing then you need to be able to measure it. Do you need to monitor the timing of each and every measurement while running? Could you measure and certify the timing of the equipment before using it? Got a cheap oscilloscope? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Computer time, independent of date
benchpress also uses System.CPUTime -- is that what you are looking for? I'm writing a program that will read medical signs from many patients. It's important to have a precise measure of the time interval between some signs, and that can't depend on adjustments of time. (Supose my software is running midnight at the end of a year with leap seconds. I would get wrong time intervals.) System.CPUTime.getCPUTime is supposed to give cpu time my program have used. However, something like a platform independent way to know for how long the computer has been turned on would do all I need. Or, maybe, how much has elapsed since the program started. Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Hello Mauricio, Friday, January 9, 2009, 4:01:18 PM, you wrote: computer has been turned on would do all I need. Or, maybe, how much has elapsed since the program started. i think you should look into system counters (if you on windows). for example, task managet in vista shows time since reboot, i think that in registry it should be available in previous windowses too. at the cpu level, there is cpu ticks counter, it should be readable via special libraries -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Don't know if it might help but: http://en.wikipedia.org/wiki/RDTSC cabal install rdtsc http://hackage.haskell.org/packages/archive/rdtsc/1.1.1/doc/html/System-CPUTime-Rdtsc.html Regards, CS 2009/1/9 Bulat Ziganshin bulat.zigans...@gmail.com Hello Mauricio, Friday, January 9, 2009, 4:01:18 PM, you wrote: computer has been turned on would do all I need. Or, maybe, how much has elapsed since the program started. i think you should look into system counters (if you on windows). for example, task managet in vista shows time since reboot, i think that in registry it should be available in previous windowses too. at the cpu level, there is cpu ticks counter, it should be readable via special libraries -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: Computer time, independent of date
Hello Cetin, Friday, January 9, 2009, 4:29:04 PM, you wrote: yes, i mean this lib but forget its name :) thank you Don't know if it might help but: http://en.wikipedia.org/wiki/RDTSC cabal install rdtsc http://hackage.haskell.org/packages/archive/rdtsc/1.1.1/doc/html/System-CPUTime-Rdtsc.html Regards, CS 2009/1/9 Bulat Ziganshin bulat.zigans...@gmail.com Hello Mauricio, Friday, January 9, 2009, 4:01:18 PM, you wrote: computer has been turned on would do all I need. Or, maybe, how much has elapsed since the program started. i think you should look into system counters (if you on windows). for example, task managet in vista shows time since reboot, i think that in registry it should be available in previous windowses too. at the cpu level, there is cpu ticks counter, it should be readable via special libraries -- Best regards, Bulat mailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Mauricio ha scritto: benchpress also uses System.CPUTime -- is that what you are looking for? I'm writing a program that will read medical signs from many patients. It's important to have a precise measure of the time interval between some signs, and that can't depend on adjustments of time. (Supose my software is running midnight at the end of a year with leap seconds. I would get wrong time intervals.) What precision do you need? On a recent POSIX platform you can use the real time clock: http://linux.die.net/man/2/clock_gettime http://www.opengroup.org/onlinepubs/009695399/functions/clock_getres.html CLOCK_MONOTONIC is what you need. [...] Regards Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Cetin Sert ha scritto: Don't know if it might help but: http://en.wikipedia.org/wiki/RDTSC cabal install rdtsc http://hackage.haskell.org/packages/archive/rdtsc/1.1.1/doc/html/System-CPUTime-Rdtsc.html Note that the use of RDTSC register has some issues on multicore CPU. More info at: http://en.wikipedia.org/wiki/Rdtsc Regards Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Computer time, independent of date
Both wikipedia and hackage rdtsc packages have lot of warnings regarding things I'm not able to control. It seems it doesn't work with many platforms, be it older or multi-core, hibernating computers. yes, i mean this lib but forget its name :) thank you Don't know if it might help but: http://en.wikipedia.org/wiki/RDTSC cabal install rdtsc http://hackage.haskell.org/packages/archive/rdtsc/1.1.1/doc/html/System-CPUTime-Rdtsc.html computer has been turned on would do all I need. Or, maybe, how much has elapsed since the program started. i think you should look into system counters (if you on windows). for example, task managet in vista shows time since reboot, i think that in registry it should be available in previous windowses too. at the cpu level, there is cpu ticks counter, it should be readable via special libraries ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
On Fri, 09 Jan 2009 11:01:18 -0200, you wrote: I'm writing a program that will read medical signs from many patients. It's important to have a precise measure of the time interval between some signs, and that can't depend on adjustments of time. (Supose my software is running midnight at the end of a year with leap seconds. I would get wrong time intervals.) If you really need that level of accuracy, there is nothing available on an off-the-shelf machine that will do the job. You need an independent timekeeping source of some kind, one that is not subject to the vagaries of reboots and other upsets. Perhaps the simplest and least expensive of these is a computer-compatible GPS time receiver. Since GPS works on GPS time (which has a constant offset from International Atomic Time), rather than UTC, you avoid having to deal with leap seconds and the like. I haven't tried doing it myself, but I know that most recent-vintage GPS units have a computer interface over which you can download the current GPS time from the device. There are many other kinds of GPS time receivers available, including ones that plug directly into a PC slot. Here's one that I found using a Google search on GPS time receiver: http://www.franklinclock.com/gps_receivers.htm The prices range anywhere from a couple of hundred dollars for consumer-grade equipment to many thousands for high-reliability devices. The only drawback to this approach that I can think of is if the hospital is in an urban area with lots of tall buildings, it might be difficult to obtain a GPS signal of high enough quality. Some of the purpose-built GPS time receivers have better antennas than a consumer-grade GPS device. Steve Schafer Fenestra Technologies Corp http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Steve Schafer wrote: On Fri, 09 Jan 2009 11:01:18 -0200, you wrote: I'm writing a program that will read medical signs from many patients. It's important to have a precise measure of the time interval between some signs, and that can't depend on adjustments of time. (Supose my software is running midnight at the end of a year with leap seconds. I would get wrong time intervals.) If you really need that level of accuracy, there is nothing available on an off-the-shelf machine that will do the job. You need an independent timekeeping source of some kind, one that is not subject to the vagaries I'm not sure that the original question implied *that* level of need. Linux has High-Resolution Timers (HRTs) that may be appropriate. See the manpage for clock_gettime(), which defines these HRTs: CLOCK_REALTIME System-wide real-time clock. Setting this clock requires appropriate privi- leges. CLOCK_MONOTONIC Clock that cannot be set and represents monotonic time since some unspeci- fied starting point. CLOCK_PROCESS_CPUTIME_ID High-resolution per-process timer from the CPU. CLOCK_THREAD_CPUTIME_ID Thread-specific CPU-time clock. CLOCK_MONOTONIC, in particular, looks suitable. Using it could be a matter of just a few quick likes in FFI. I don't know if Windows has similar features. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
John Goerzen ha scritto: Steve Schafer wrote: On Fri, 09 Jan 2009 11:01:18 -0200, you wrote: I'm writing a program that will read medical signs from many patients. It's important to have a precise measure of the time interval between some signs, and that can't depend on adjustments of time. (Supose my software is running midnight at the end of a year with leap seconds. I would get wrong time intervals.) If you really need that level of accuracy, there is nothing available on an off-the-shelf machine that will do the job. You need an independent timekeeping source of some kind, one that is not subject to the vagaries I'm not sure that the original question implied *that* level of need. Linux has High-Resolution Timers (HRTs) that may be appropriate. See the manpage for clock_gettime(), which defines these HRTs: [...] CLOCK_MONOTONIC, in particular, looks suitable. Using it could be a matter of just a few quick likes in FFI. There is also an available package on Hackage: posix-realtime. I don't know if Windows has similar features. http://msdn.microsoft.com/en-us/library/ms632592(VS.85).aspx and QueryPerformanceCounter, in detail. Unfortunately, documentation is really bad, and it is not really clear what high-resolution performance counter means. -- John Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Here's a basic draft project for clock_gettime(CLOCK_MONOTONIC, ...) http://sert.homedns.org/hs/mnsec/ http://sert.homedns.org/hs/mnsec/dist/mnsec-1.0.0.tar.gz It could be extended to cover other clock types than just monotonic. Regards, CS 2009/1/9 John Goerzen jgoer...@complete.org Steve Schafer wrote: On Fri, 09 Jan 2009 11:01:18 -0200, you wrote: I'm writing a program that will read medical signs from many patients. It's important to have a precise measure of the time interval between some signs, and that can't depend on adjustments of time. (Supose my software is running midnight at the end of a year with leap seconds. I would get wrong time intervals.) If you really need that level of accuracy, there is nothing available on an off-the-shelf machine that will do the job. You need an independent timekeeping source of some kind, one that is not subject to the vagaries I'm not sure that the original question implied *that* level of need. Linux has High-Resolution Timers (HRTs) that may be appropriate. See the manpage for clock_gettime(), which defines these HRTs: CLOCK_REALTIME System-wide real-time clock. Setting this clock requires appropriate privi- leges. CLOCK_MONOTONIC Clock that cannot be set and represents monotonic time since some unspeci- fied starting point. CLOCK_PROCESS_CPUTIME_ID High-resolution per-process timer from the CPU. CLOCK_THREAD_CPUTIME_ID Thread-specific CPU-time clock. CLOCK_MONOTONIC, in particular, looks suitable. Using it could be a matter of just a few quick likes in FFI. I don't know if Windows has similar features. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Computer time, independent of date
Linux has High-Resolution Timers (HRTs) that may be appropriate. See the manpage for clock_gettime(), which defines these HRTs: [...] CLOCK_MONOTONIC, in particular, looks suitable. Using it could be a matter of just a few quick likes in FFI. I don't know if Windows has similar features. http://msdn.microsoft.com/en-us/library/ms632592(VS.85).aspx and QueryPerformanceCounter, in detail. Going from GetProcessTimes, which I found in ghc code in libraries/base/System/CPUTime.hsc, I was just able to find this in that same site: http://msdn.microsoft.com/en-us/library/ms724408(VS.85).aspx Seems simpler. Since linux (and unix?) have clock_gettime and windows has this GetTickCount, maybe it could be possible to add getSystemCPUTime to System.CPUTime. Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
On Fri, 09 Jan 2009 09:28:49 -0600, you wrote: I'm not sure that the original question implied *that* level of need. I can't imagine being worried about leap seconds yet at the same time being willing to accept the potential vagaries of any of the built-in clocks. Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Computer time, independent of date
Is there an alternative? Something like how much time has passed since the program has started would be great. Have a look at benchpress on hackage. But benchpress uses Data.Time.Clock.getCurrentTime. I understand that is dependent from configuration. It's okay to benchmark a fast application, but mine will be running for days, so it would not be reliable. Best, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Computer time, independent of date
Mauricio wrote: But benchpress uses Data.Time.Clock.getCurrentTime. I understand that is dependent from configuration. It's okay to benchmark a fast application, but mine will be running for days, so it would not be reliable. benchpress also uses System.CPUTime -- is that what you are looking for? Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
