Hi - I'm trying to choose a microcontroller for a project I'm working on. Originally I had been thinking about using a 20Mhz Atmel AVR, such as an ATMEGA168, but I became worried about the raw computing power of the AVR, as one of the main roles of this chip will be to do alot of 16 bit multiplication and trig at a fairly high speed. So I've been looking at using an ARM - specifically the Atmel AT91SAM7A3 looks very interesting to me. It's clocked 3 times as fast as the ATMEGA168, but I expect that isn't a good way at all to compare it's ability to handle this task to the AVR's. Is there any good way to make a comparison for this application without benchmarking the chips? Thanks, -Michael J. Noone
How to compare computing power of microcontrollers?
Started by ●August 30, 2005
Reply by ●August 30, 20052005-08-30
Michael J. Noone wrote:> Hi - I'm trying to choose a microcontroller for a project I'm working > on. Originally I had been thinking about using a 20Mhz Atmel AVR, such > as an ATMEGA168, but I became worried about the raw computing power of > the AVR, as one of the main roles of this chip will be to do alot of 16 > bit multiplication and trig at a fairly high speed. So I've been > looking at using an ARM - specifically the Atmel AT91SAM7A3 looks very > interesting to me. It's clocked 3 times as fast as the ATMEGA168, but I > expect that isn't a good way at all to compare it's ability to handle > this task to the AVR's. Is there any good way to make a comparison for > this application without benchmarking the chips? Thanks, > > -Michael J. NooneARM is also a 32 bit CPU, vs. 8 bits for the AVR. So for instance, to do 32 bit arithmetic operations on AVR takes 4 instructions/clocks, while the ARM will do a 32 bit operation in one instruction/clock. For floating point stuff, things are more complicated, but still the advantage goes to the 32-bit CPU. So for 32-bit integer arithmetic anyway, a 60MHz ARM would be roughly 12 times faster than an AVR. -- Good day! ________________________________________ Christopher R. Carlen Principal Laser&Electronics Technologist Sandia National Laboratories CA USA crcarleRemoveThis@BOGUSsandia.gov NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.
Reply by ●August 30, 20052005-08-30
On 2005-08-30, Chris Carlen <crcarleRemoveThis@BOGUSsandia.gov> wrote:> Michael J. Noone wrote: >> Hi - I'm trying to choose a microcontroller for a project I'm working >> on. Originally I had been thinking about using a 20Mhz Atmel AVR, such >> as an ATMEGA168, but I became worried about the raw computing power of >> the AVR, as one of the main roles of this chip will be to do alot of 16 >> bit multiplication and trig at a fairly high speed. So I've been >> looking at using an ARM - specifically the Atmel AT91SAM7A3 looks very >> interesting to me. It's clocked 3 times as fast as the ATMEGA168, but I >> expect that isn't a good way at all to compare it's ability to handle >> this task to the AVR's. Is there any good way to make a comparison for >> this application without benchmarking the chips? Thanks, >> >> -Michael J. Noone > > > ARM is also a 32 bit CPU, vs. 8 bits for the AVR. So for instance, to > do 32 bit arithmetic operations on AVR takes 4 instructions/clocks, > while the ARM will do a 32 bit operation in one instruction/clock. > > For floating point stuff, things are more complicated, but still the > advantage goes to the 32-bit CPU. > > So for 32-bit integer arithmetic anyway, a 60MHz ARM would be roughly 12 > times faster than an AVR.At least. Rember the ARM has a barrel-shifter that can be used in "parallel" with an arithmetic operation. IOW, A = A + B<<3; Is a single instruction on an ARM. If A and B are 32-bit ints, I doubt that can be translated into to 4 AVR instructions. -- Grant Edwards grante Yow! I just remembered at something about a TOAD! visi.com
Reply by ●August 30, 20052005-08-30
If you don't have hardware for both, I would write a piece of assembly code "on paper". This code should be represntative of a function that you will be doing for your application (ie. 16 bit multiplication and trig). And add up the number of clock cycles it would take each processor to run the same piece of code. This calculations assumes each processor has similar instructions and the compilers you use have a similar optimization routine. You know the # of clock cycles and the frequency, you can then evaluate which processor has a better performance for your application. It is time consuming, but without looking at the Datapath / Instruction cycles you can't evaluate the performance. Example: a processor may run at a faster clock frequency, but if the instructions you are using aren't pipelined well your just burning up power and not gaining performance. Multiplication tends to be one of the instructions that is poorly pipelined in smaller cpus. So the # of instructions that MULT takes might be a good enough benchmark for your application. Good Luck, Eric
Reply by ●August 30, 20052005-08-30
On 30 Aug 2005 09:01:28 -0700, the renowned "Eric" <ericjohnholland@hotmail.com> wrote:>If you don't have hardware for both, I would write a piece of assembly >code "on paper". This code should be represntative of a function that >you will be doing for your application (ie. 16 bit multiplication and >trig). And add up the number of clock cycles it would take each >processor to run the same piece of code. > >This calculations assumes each processor has similar instructions and >the compilers you use have a similar optimization routine. > >You know the # of clock cycles and the frequency, you can then evaluate >which processor has a better performance for your application. > >It is time consuming, but without looking at the Datapath / Instruction >cycles you can't evaluate the performance. > >Example: a processor may run at a faster clock frequency, but if the >instructions you are using aren't pipelined well your just burning up >power and not gaining performance. > >Multiplication tends to be one of the instructions that is poorly >pipelined in smaller cpus. So the # of instructions that MULT takes >might be a good enough benchmark for your application. > >Good Luck, >EricIIRC, the AVR has an 8 x 8 multipler, wheras the ARM core has a wider multiplier (32 x 8?) and microcode to do 32 x 32 multiplies. By the time you assemble all the partial products with the AVR, the difference in speed might be quite large for multiply. Personally, I'd write a little chunk or two of code and simulate it. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Reply by ●August 30, 20052005-08-30
Eric wrote:> If you don't have hardware for both, I would write a piece of assembly > code "on paper". This code should be represntative of a function that > you will be doing for your application (ie. 16 bit multiplication and > trig). And add up the number of clock cycles it would take each > processor to run the same piece of code. > > This calculations assumes each processor has similar instructions and > the compilers you use have a similar optimization routine. > > You know the # of clock cycles and the frequency, you can then evaluate > which processor has a better performance for your application. > > It is time consuming, but without looking at the Datapath / Instruction > cycles you can't evaluate the performance. > > Example: a processor may run at a faster clock frequency, but if the > instructions you are using aren't pipelined well your just burning up > power and not gaining performance. > > Multiplication tends to be one of the instructions that is poorly > pipelined in smaller cpus. So the # of instructions that MULT takes > might be a good enough benchmark for your application.Good advice from Eric there. You should also be aware of the cost constraints of your project (is this a one off or do you need to make millions of devices?). This will also determine whether the effort you expend in finding the processor is better than going wity one that may be overkill in terms of obvious performance advantage. -- ******************************************************************** Paul E. Bennett ....................<email://peb@amleth.demon.co.uk> Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/> Mob: +44 (0)7811-639972 Tel: +44 (0)1235-811095 Going Forth Safely ....EBA. http://www.electric-boat-association.org.uk/ ********************************************************************
Reply by ●August 30, 20052005-08-30
"So for instance, to do 32 bit arithmetic operations on AVR takes 4 instructions/clocks, while the ARM will do a 32 bit operation in one instruction/clock. " I would think its more like a 12-1 ratio, 32 bit add on a 8 bit machine generally requires loads and stores inbetween each 8 bit add
Reply by ●August 30, 20052005-08-30
http://www.keil.com/benchmks/tm_c51_v7_small.asp Don't know about AVR's but the above is a good site to compare the differences between processing power between 8051 and ARM's, it allows you to type in the frequency of each part and it will show you how long a 8,16 or 32 bit add/sub/mul will take as well as float trig functions.