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Subject:  Another performance comparison Z8 Encore! vs ATmega16

 
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Having published a performance comparison showing the ATmega64 to be 
four times faster than the Z8 Encore!, I am obviously concerned that 
I've done something wrong and falsely denigrated the Z8 Encore!.  Of 
course, performance isn't always an issue, so this isn't necessarily 
such a big deal.
 
Porting my operating system, ECROS, to the ATmega64 has been on my 
list of things to do and I got around to starting it today.  I've 
got to the point where another performance comparison is possible.  
I'm afraid the factor of four holds.
 
I have the ECROS scheduler, timers and event mechanism working.  I'm 
not using stream I/O and I've compiled out the execution profiler, 
so it's a lean and fast configuration.  I have two tasks, both at 
the same (high) priority.  One gets an event every 500 ms from a 
repeating timer and flips an LED so it flashes once per second.  
This is just to make sure that the OS timers are working.  The other 
task has an event set which it never clears and therefore runs over 
and over again.  It also flips an LED.  I am measuring the frequency 
of the second LED flashing.  This gives me a measure of the task 
switching time of the OS.  In other words, I can time the code path 
from where the always-ready task flips the LED back into the 
scheduler, through all the scheduler's internal workings (updating 
timers and picking the next, usually the same, task) and back to the 
LED flip point in the task again.  Since the task does so little, 
most of this time is used by the scheduler.
 
Z8 Encore! at 18.432 MHz with ZDS II 4.8.0 --- 52 us (measured 9.60 
kHz)
ATmega64 at 15.36 MHz with AVR-GCC 3.3.2 --- 12.5 us (measured 39.9 
kHz)
 
Since this code has nothing in common with the Dhrystone code, the 
conclusion seems inescapable.  If you're looking for best execution 
speed at a given cost and power point, the Z8 Encore! is unlikely to 
be your best choice.
 
As compared to the Z8 Encore!'s four symmetrical timer/counters, the 
ATmega64 has two 8 bit timer/counters which are slightly different 
and two 16-bit timer/counters.  I think they can do some tricks that 
the Z8 Encore! can't, but I have to admit it's a chore figuring each 
one out separately.  I think the Z8 Encore! is easier to understand 
and use in this regard.
 
Graham.
http://www.ecrostech.com