High-end AVR vs. low-end ARM?

ARM chips like the NXP LPC2000 can be cheaper than high-end AVRs, and offer much more performance. However, they consume more power and could work out more expensive by the time they are put on a PCB, because of the requirement for two supplies.

Leon

d ARM

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Hi,

@ Leon, I agree in everything but one, the power consumption. For example the mentioned LPC2000 can run with 40 mAs @ 70 MHz (2103), my guess would be you need 10 AVRs, running @ 16 MHz to match the performance in computing. AFAIK they need more than 4 mAs @ 16 MHz. On the other hand there is a HUGE difference in standby current. AVRs at least the older ones can go into standby mode at or below 1uA, if one if the ARM devices gets hot the standby current exceeds 100 uAs easily.

There is another reason why to stick with AVR, simplicity. If you are familiar with AVR, you can finish your project a lot faster than using an ARM. Given a scenario where you start a new project and you wonder whether the AVR will be powerful enough, go with the ARM, it is going to provide more for he money. If your deadline is the most important topic and the AVR is powerful enough, spend the extra money and stay with the 8-bit.

As for AVR32, in case you were thinking about that one, there is no real reason I would know why to start with that device. Use a Cortex- M3 device instead the upcoming standard.

AnSchwob

ARM

on

Just one more thing. The 1.8V to 5.5V operating range for the AVR is very useful for battery devices. You usually need higher than 1.8V, even for ARM with build-in regulator.

As soon as code size goes over 64K, then the simplicity of the AVR vanishes. Not having 24bit or 32bit pointers causes all sorts of problems. Also if one need to execute code from RAM space, then AVR is a no go. The Cortex-M3 devices tend to have a built in regulator for gnerating all the needed supplies from one supply. They are also a LOT cheaper when one starts looking at >= 128K flash . The Cortex-M3 devices has removed a lot of the complexity one has to deal with when using the ARM7 and ARM9 MCUs.

ATMEGA128-16AU is US$15 while a LM3S1607-IQR50 is US$5 in single quantities at Digikey. The ATMEGA128 is 16MHz, 8Bit with 128K of flash. The LM3S1607 is 50MHz, 32bit with 128K of flash.

Agreed.

Regards Anton Erasmus

Let's see,

Where do I get the Cortex-M3 flash chip with

• Lower power consumption than any existing Cortex-M3 chip

• Single 1,8V +/- 10% power-supply for CORE *AND* I/O?

• 5V VCC , desirable for motor control?

• debug support allowing you to read/write internal registers without stopping the MCU.

• High Speed USB

• Free Eclipse/GCC tool directly supported by the silicon vendor

• Sustained 33 DSP MIPS when doing vector sums for(sum=0; i = 0; i < n; i++) sum = sum + C[i] * X[i];

• Migration path to low cost versions supporting Linux.

• Same H/W tools as the AVR (JTAG-ICE Mk II & STK600)

• Trace capable emulator at below 0 (AVRONE)

Googling does not give any clue...

--
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

How much flash, with the above combinations ?

-jg

The full combination does not exist. Just listed some properties, that could make people want to think twice about focusing 100% on CM3.

UC3L = 1.8V VCC UC3C = 5V UC3A3 = High Speed USB UC3B & UC3L should be lower power than CM3 UC3A/C has 66 MHz operation and thus 33 DSP MIPS AP7 runs Linux, Need Cortex-A8 for this and that ain't cheap.

In the end, it will be the right combination of peripherals which will be key to the decision.

--
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

Well, duuuuuh. It's an impossible question!

Yep, but I think people get the hint ;-)

--
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

You can compare Cortex-M3 to AVR32 UC3A and UC3B series, but not to AP7(hi-speed usb, mmu, linux) - it's a different class of devices. We also don't compare Intel Core2Duo to AVR ;)

--
voices (at) zrgnyyvpenva (dot) pbz [ROT13]

googling doesn't give you a clue for 1.8V, 5V AVR32s either....

ARM

on

If you need really cheap and your watching every penny then ARM's are still higher price then low end AVR's. Cortex has low power similar to AVR and MSP430's, running and standby, and operate down to 2V. ARM's tend to come in bigger packages and require more external parts (caps), in general. As a wild guess I would say 90% of High end AVR' applications could switch to an ARM. There are some ultra low power applications where AVR and MSP430 are still king and there is no ARM substitute.

Well that proves that google doesn't know everything :-)

All things above mentioned in the offical UC3 presentation, The average Joe won't see UC3L/UC3C/UC3A3 until beginning of next year.

The technology behind the 1.8V devices is already available in AT91SAM7L. The SAM7L runs the flash down to 1,55V.

--
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

snipped-for-privacy@u18g2000pro.googlegroups.com...

Ok, the 7L are nice, though wish they expand the family

I've noticed in the Atmel slides packages they say FIR filter is 11 times faster then on a CortexM3. That is hard to believe, not sure why, Cortex is 2 cycle MAC, AVR32 is single cycle, maybe with the 2 wait states on Cortex FLASH they came up with that number?

• Sustained 33 DSP MIPS when doing vector sums for(sum=3D0; i =3D 0; i < n; i++) sum =3D sum + C[i] * X[i];

the 33 MIPS is at what clock speed?

meddelandetnews: snipped-for-privacy@u18g2000pro.googlegroups.com...

Ok, the 7L are nice, though wish they expand the family.

==> There is a new family in the works with more SRAM.

I've noticed in the Atmel slides packages they say FIR filter is 11 times faster then on a CortexM3. That is hard to believe, not sure why, Cortex is 2 cycle MAC, AVR32 is single cycle, maybe with the 2 wait states on Cortex FLASH they came up with that number?

==> Not only that. I am not sure about 11 times though.

You win by having * 1 clock cycle load instructions. Cortex-M3 implementations are at least 2, maybe more If running from flash, then there will be plenty of clocks. The AVR32 with the AHB will probably use two clocks to read from the flash at 66 MHz. Furthermore, this is non blocking in some cases since the core can read instructions from the intruction queue instead of from the flash. * The ability to use the upper part of the 32 bit register for MAC instructions, so you load TWO samples/coefficients in a single clock cycle.

The unroled loop then becomes:

LOAD 1 clock LOAD 1 clock MAC 1 clock MAC 1 clock

• The hidden Accumulator The register file on a low end risc processor normally only have two read ports. You cannot do A = A + C*X in a single clock because you need to read A,C and X in the same clock cycle.

The AVR32 has a "hidden" accumulator (patented) which allows you to use the two read ports for C and X

After the last MAC, you write the accumulator back to the register file, adding one clock latency

• The AVR32 runs with 1 waitstate, while the STM32 runs with 2.

• Sustained 33 DSP MIPS when doing vector sums for(sum=0; i = 0; i < n; i++) sum = sum + C[i] * X[i];

• The last feature is instructions which handle saturation the way a DSP should, and this has to be handled manually in other RISCs like CM3

the 33 MIPS is at what clock speed?

==> 66 MHz (with a 100% unrolled loop) I.E: n = 6 =>

LOAD 1 clock LOAD 1 clock MAC 1 clock MAC 1 clock LOAD 1 clock LOAD 1 clock MAC 1 clock MAC 1 clock LOAD 1 clock LOAD 1 clock MAC 1 clock MAC 1 clock ; Hidden writeback: 1 clock

--
-- 
Best Regards,
Ulf Samuelsson
ulf@a-t-m-e-l.com
This message is intended to be my own personal view and it
may or may not be shared by my employer Atmel Nordic AB

Indeed, people are still spreading lies about Cortex-M3 as usual.

Cortex-M3 loads are 2 cycles unless the next instruction is a load or store, in which case it is 1 cycle. So a sequence of N loads takes N+1 cycles.

This is the same trick as the ARM9E introduced a long time ago.

The Luminary Cortex-M3 cores run with 0 wait states. But even with a wait state you don't necessary see a slowdown if the fetch width is at least 64 bits (3-4 Thumb-2 instructions). Waitstates primarily slowdown branches.

Actually Cortex-M3 has a saturate instruction.

On Cortex-M3 this would take the following sequence:

LDRH r2, [r0,#0] LDRH r3, [r0,#2] LDRH r4, [r0,#4] LDRH r5, [r1,#0] LDRH r6, [r1,#2] LDRH r7, [r1,#4] MLA r8,r2,r5,r8 MLA r8,r3,r6,r8 MLA r8,r4,r7,r8

The LDRHs take 7 cycles (6 + 1), the MLAs take 6 cycles, or in total 26 cycles. That is exactly twice as slow as AVR32 on the above code. So the claim of 11 times slower is a total lie. Those Atmel marketeers should be ashamed of themselves.

Wilco

ioe.org...

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11

Ok, I took the atmel published FIR filter cycle count and the STM FIR filter cycle count both from their websites (using their optimized in house DSP packages)

of course both don't give data on the same size FIR filter, so I have to normalize...

For Atmel, a 64 point, 24 tap,41 outputs FIR takes 2,439 cycles, which is 41*24 =3D 984 MACs, for a cycle/MAC ratio of 2.478 cycles/MAC

For STM Cortex at full speed 2 wait states, 63 point 32 tap, 32 output FIR takes 3929 cycles, which is 32*32 =3D 1024 MACs for a ratio of 3.83 cycles/MAC (2 wait states)

a difference of 1.54X

at zero wait states ( below 24Mhz) STM reports 3478 cycles

so 3.396 cycles/Mac (0 wait states), a difference of 1.37 times

And you are comparing 3 MACs with 6 MACs.

6 MACs from memory using AVR32 = 13 clocks. 6 MACs from memory using CM3 = 52 clocks or 4 x difference.

--
Best Regards,
Ulf Samuelsson
ulf@a-t-m-e-l.com
This message is intended to be my own personal view and it
may or may not be shared by my employer Atmel Nordic AB

cycles.

No, read again. It's 13 cycles to do 3 MACs, so 26 to do 6 MACS.

Wilco