Short answer is 'maybe.'
You can see how the clock tree is set up by reading the RCC_CFGR registers.
*If* it is set to use an internal clock (say HSI or MSI) you can can
calculate the speed based on how the registers are set up. If however it is
using an external crystal (HSE) you can't really know what the speed is.
ARM suggests in their CMSIS spec that you maintain a global variable that
has the clock speed in it.
In my clock utility code (which has shown up several times in a variety of
the examples directories) I have a msleep(t) function which sleeps for 't'
milliseconds sort of. It uses the SysTick timer and it counts ticks but if
you wanted to wait for 1 millisecond you calling it you may wait for
anywhere between .001 and 1 mS depending on where in the count you caught
it. So for delays the accuracy is 100/length percent (10 percent for a 10mS
pause, 1% for a 100mS pause, etc).
For much more accurate delays (and you still need to know what the core
clock is) you can set a timer and then execute a WFI (wait for interrupt)
instruction. That will move to the next instruction on return from
interrupt. Of course if the interrupt *wasn't* your timer you should
probably go back to sleep, and if you call WFI *after* the interrupt has
fired you will wait forever. The alternative is to simply busy wait on the
interrupt flag while not worrying about it firing. Then at least you always
proceed, but if you take an interrupt while waiting for something like
reading a serial character or dealing with USB your delay again may be
messed up.
Does that help?
--Chuck
On Sun, Apr 16, 2017 at 4:39 PM, kristoff <krist...@skypro.be> wrote:
> Hi,
>
>
> I may be wrong but -as far as I see it- there is no "delay_ms" (or
> equivalent) in libopencm3.
>
>
> I started doing some more work on my FPGA programmer on a STM32F103 and
> -to port the arduino library to libopencm3- I need both the "delay_ms"
> and "millis" functions.
> Therefor I am working on a generic library for this, using the cortex-M
> "systick" interrupt.
>
>
> Question:
> As the reload-value used by systick is directly related to the
> clockspeed of the CPU, is there in libopencm3 a generic way to determine
> the clockspeed of the CPU?
> My goal is to determine if the speed of the CPU has been changed.
>
>
> For the STM32, I found there are a number of external variables that I
> might use (rcc_ahb_frequency, rcc_apb1_frequency and rcc_apb2_frequency)
> but I guess these are specific for that processor.
>
>
> Cheerio! kr. Bonne.
>
>
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