Thread: Timing measurements on windows

There are several functions of different levels of portability:
1. clock() - generic function that returns fairly precise timings.
2. QueryPerformanceCounter/QueryPerformanceCounterFrequency
3. RDTSC processor instruction.

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Mats

There is also timeGetTime() which returns a very exact millisecond clock (I used it to create a loop that looped for exactlly 1s).

What sort of timer resolution were you looking for? (that determines what timer to use)

The thing to remember about MS OS's is the OS message queue can ignore timer msgs (and paint msgs are concatinated).

For this reason timers are not overly accurate.

Originally Posted by Elysia

There is also timeGetTime() which returns a very exact millisecond clock (I used it to create a loop that looped for exactlly 1s).

Minimum resolution is >5ms.

I would use QueryPerformanceCounter/QueryPerformanceCounterFrequency (if available).

You can also set the resolution for timeGetTime; default resolution on Windows 95 is one ms!
Anyway, try which solution works best.

QueryPerformanceCounter is much more precise than 1ms, it's at the very least capable of milliseconds, and on modern machines it often uses better timers, such as PM timer, APIC timer or some other high-res timer.

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Mats

> after after I have sent a packet to my embedded device, some mechanism
> to count how many milliseconds have passed since I sent the packet.
Are you attempting some kind of 'time-based' flow control to regulate how much data you send to the device?

I actually read (perhaps mistakenly) the original post to want to do some sort of performance measurement. But other options are of course possible - like so many posts here, the "purpose of the question" is not explained, and we have to guess what is the right solution to the question.

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Mats

How do you do the "receive from USB" function? Are you using a file-read, or some other interface?

I'm thinking that you want to do a WaitForSingleObject() with a timeout of 250ms.


At the same time, I guess you would need to read the data no matter what - just that if it arrives late (or there isn't enough data there) you may want to discard the actual data. So perhaps you need to figure out what happens when/if data is late.

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Mats

You could also use Sleep to sleep for 250ms. This will not take any cpu power, and it's also easier than WaitForSingleObject so it might be a better idea.

Originally Posted by Elysia

You could also use Sleep to sleep for 250ms. This will not take any cpu power, and it's also easier than WaitForSingleObject so it might be a better idea.

But that means that the application CAN'T process any data that comes in during this time. And it's only "easier" because you have to type less. A Sleep() is actually implemented as a WaitForSingleObject() [or some varation of that], where it's waiting for a Timer Event.

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Mats

That's why we usually have threads.
If it's a Window app, you need a thread anyway since the main thread needs to process messages.