[ell-i-developers] Re: ELL-i-Arduino Delay functions and interrupt disable
- From: Pekka Nikander <pekka.nikander@xxxxxx>
- To: ell-i-developers@xxxxxxxxxxxxx
- Date: Fri, 21 Feb 2014 08:24:55 +0200
> [...] so it uses the function delayMicroseconds() from
> Arduino to read fast but not continuously, and this function is not be
> tested in our environment according to Pekka. Can someone test if this
> function is doing what it should? Probably the problem is here.
I think it is best that if you check it, with oscilloscope. Just create a
simple sketch that toggles an I/O with delayMicroseconds in between, and
measure if the time is right with different values.
It is also a good idea to have a look at the source code in Ell-i/Arduino.git,
in hardware/ell-i/stm32/cores/arduino/wiring_time.h. (Grep is your friend.)
Based on my quick look, it is no wonder if it does not work correctly.
> I don´t know if that works in our environment, if it does, please tell
> me how many nanoseconds each nop should take. They say that one cycle
> at 16 Mhz is 62.5 nanoseconds. I don´t know what is the frequency of
> our processor at the moment, so it would be interesting to know.
Relying on nops is a very bad practise. The compile time frequency is
available in F_CPU define. However, on the ST Cortex-M0 it is possible to
change the frequency on the fly...
A much better approach would be to use one of the timer/counters to read the
pin at fixed periods, independent of the CPU. For that there is the Arduino
shiftIn API. I seem to have implemented it using delay(), but it has never
been tested. A good exercise would be to rewrite the shiftIn API with a
timer/counter.
> noInterrupts() and interrupts() that is a more portable version
They are defined in wiring_constants.h. They should work.
In general, at this staged of the development it is always a good idea to read
the source code.
--Pekka
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