How to delay until a next increment of time occurs ?

[Rob Gaddi]

On 11/13/19 1:26 PM, Dietmar Schwertberger wrote:
> On 13.11.2019 21:20, R.Wieser wrote:
>>> 300us is getting on towards realtime.
>> Not really.  Translated to a frequency (toggeling the pin) it would be just
>> 1.6 KHz.   Thats rather slow for an ARM machine running on 1.4 Ghz (about a
>> million times as fast).
> 
> It *is* real-time...
> Real-time is not about speed, but about guaranteed timing.
> 

Yeah, that's always the conversation, but at the end of the day "realtime" is 
always a question of "by how much".  Do you really need to be hard periodic with 
0 ns slop in either direction?  Can you afford to come in early but not late? 
By 10%?  By 1%?  By .01%?

If you can afford 1% and you need a 1 second interval, you're only asking for 10 
ms and in practice even a giant preemptive non-RT OS like Linux can do it for 
you.  If you can only afford 1% on a 300 us interval then your lack of rigid 
control over what happens on your processor is a real problem and you're better 
off bare metal on a dedicated $2 Cortex-M than with random timeslices of the 
1.4GHz beast on the rPi.

Is what I was shorthanding with "realtime".


-- 
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order.  See above to fix.