Re: Atmega128 or MSP430 for low power, decent performance?

"David Brown" <david@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> skrev i meddelandet
news:45045139$0$19464$8404b019@xxxxxxxxxxxxxxxxxx
steve wrote:
Ulf Samuelsson wrote:

Most AVR instructions will take 1 clock cycle

with the unrealistic assumption all the dataspace you need can be
accomodated by the 32 registers, yes (and the same can be said of the
MSP430) but otherwise 2 clock cycles is much more realistic


Microcontroller manufacturers always seem to be very optimistic about
claims like "most instructions will take 1 clock cycle". Perhaps by
"most" they mean most in the instruction code space, or perhaps most
different opcode names - it certainly never seems to refer to most
instructions in real programs (either in terms of the code written, or in
terms of the instructions executed).

Yes, that is exactly what it measn.
You cannot judge how many cycles it uses in an application program
since no application prgrams are alike. Some try to measure instructions per
clock
using the Dhrystone benchmark, but this assumes the compiler has
not been tweaked for this specific benchmark.

And of course, it is virtually irrelevant how many clock cycles each
instruction takes - what *is* relevant is how many clock cycles common
operations take. If an operation such as moving a 16-bit integer from
memory to memory takes a single 4-clock instruction on the msp430, and 6
instructions taking 10 clocks (estimated out of my head) on the AVR, then
that's the numbers that are important for that sort of code, and it
doesn't matter that the msp430 takes more clocks per instruction. For
other types of code, the AVR may be faster.

Even that is a bot on the low level.
You need to check the complete application and also there could be features
in the peripherals which more than compensate for
any drawbacks in the core itself.


Will the part do the job within the power budget.
Can I meet the EMI goals.
Do I need extra performance/code space to allow for future upgrades?
Once this and a couple of
--
Best Regards,
Ulf Samuelsson
This is intended to be my personal opinion which may,
or may not be shared by my employer Atmel Nordic AB


.

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