How to get the interrupt time (timestamp) in kernel mode of real time Linux?

Question

Client/server communication - client is sender and server is receiver.

When the server receives the data on the ethernet interface(UDP) the kernel in the server is triggered. I am using real time LINUX on the server side. Server (ie embedded pc target) is handling interrupts to trigger the embedded pc target (containing rt Linux) to gain the attention to execute the newly arrived data.

How can I calculate the time in kernel as soon as the interrupt occurs and send the response back to the client?

Answer 1

1) If you are using an embedded linux platform, you can refer to CPU datasheet: maybe it have a set of high-speed timers. At instance, I'm using SoC based on ARM Cortex A8, it has GP timers that can be clocked up to 38.4 MHz, so I can measure execution time with ~27ns precision. Very likely, your OS would not provide such API, so you're welcome to read-write CPU registers directly from kernel driver.

2) If you are want to just estimate execution time, and nothing more, you can use one of GPIO pins of your board. Set pin up at "start", set down at "end", then watch this pin by oscilloscope, if you have one.

3) If I missunderstood you, and all that you need is timestamp of a real time (like HH:mm:ss), you can refer to RTC chip of your board. Using driver of real-time clock chip, you can read time from your kernel module. Unfortunately, you might not be able do it from interrupt service routine. Or just call do_gettimeofday and convert timeval to something human-readable via time_to_tm , if needed :)