Time to powerup

yariv008 wrote on Wednesday, July 08, 2009:

Does any one knows or have any estimation on how many clock cycles until powerup in freertos ?


rtel wrote on Wednesday, July 08, 2009:

What are you expecting the answer to this to be?  You give absolutely no information on the processor being used, the compiler being used, what your start up code is doing, how much RAM you have to be cleared, how many tasks are being created, etc. etc.

In any case, FreeRTOS adds practically no start up overhead to a standard (non RTOS) application.


jwestmoreland wrote on Wednesday, July 08, 2009:


There is definitely a distinction between power-up and when an OS is ‘operational’ - and operational can be defined in a variety of ways.

In addition to Richard’s reply - I am assuming you mean when the kernel is operational - you have to look at what you need to do for initialization, installation of interrupt vectors, look at your assembly (and count cycles) for perhaps when one task is created, the kernel is ‘started’, and the first tick interrupt occurs.  It may be somewhat difficult to calculate this depending on your target.

May I make a suggestion?

Put a scope probe on an I/O line - such as maybe going to an LED.  Toggle the LED in the timer IRQ and/or make a timer hook to do it.  With another scope probe - put that on the reset line - and use that to start the trace - by making the first probe either level or edge triggered by when the reset line goes inactive after power-on.  When the first scope probe toggles that is an estimation of when the first timer IRQ is able to respond - and thus gives an indication of the kernel being up.  You can also toggle the I/O in tasks, etc. to determine how long it takes for the 1st task completion, etc.

Of course, you will need a decent scope and access to some I/O lines to make this work - but it will give you a ‘real’ answer vs. having to do a detailed analysis with instructions and cycle-times which can be quite an exercise.


yariv008 wrote on Wednesday, July 08, 2009:

Thanks John for the answer.
I would applly your suggestion but I am currently have no HW, I am on process of choosing RTOS and try to do some comparisons between some RTOS (mainly the AT32UC3  compatible )
My question was to get some estimation on FreeRTOS in meaning of start up process as a pure RT operation system. Is there any OS process running before initial any tasks etc’ …