malfunction of atmel avr mega overclocked at 25mhz

[amazingrapist]

Get a Cortex M4, I run mine at 168MHz but it consumes about 30mA.

[ubuntututorials]

I have run a PIC micro at 33.33 MHz (rated for 20 MHz). It would not start on 33.33 MHz - I had to boot it on 24.00 MHz (which it would start on) and switch it over.

[truhlikfredy]

@ubuntututorials It was perhaps depending on what was done in boot, perhaps with different boot loader it could be done. I have found that when are you over clocking and you are using peripherals as less as possible then the device is more stable. So over clocking just the core and over clocking the whole device is different. BTW: How much MIPS you got with 33.33Mhz? The megas are 1mhz=1mips

[ubuntututorials]

@truhlikfredy 33.33 MHz = 8,332,500 instructions per second (8.3325 MIPS).

PIC16F690: not very fast; 4 cycles per instruction. I'm interested in the 24F (I've got a few) because from 8 MHz (which a PLL boosts up to 32 MHz) you get about 16 MIPs.

I was just blinking an LED at 33.33 MHz... no peripherals.

[truhlikfredy]

@ubuntututorials It was perhaps depending on what was done in boot, perhaps with different boot loader it could be done. I have found that when are you over clocking and you are using peripherals as less as possible then the device is more stable. So over clocking just the core and over clocking the whole device is different. BTW: How much MIPS you got with 33.33Mhz? The megas are 1mhz=1mips

[Manekinen]

I've overclocked some avrs to 27MHz, M32, M16, M8 and only M8 has crashed twice doing some complicated math. And it was no matter if i put 18 or 33pF caps, or even without caps - working good. But i you want to enable CKOPT fusebit for rail-to-rail you must put some caps. Have not yet tried how it will work with f generator but i guess it will be better than with crystal.

[truhlikfredy]

Ok so CPU rated for 16mhz, working with my caps 100% stable at 20mhz and maulfunting at 25mhz (56% overclocking) is just because everything else, you are sure that the reason is not too high overclocking. I bet with good caps and fuse setting you could get it running at 250Mhz.

[mast3rbug]

You have no decoupling/filtration caps on your board... Help yourself by putting some caps before.

[truhlikfredy]

Why you think there are no caps?

[mast3rbug]

I know that a CPU certified 20 MHZ can crash at 8 MHZ if you don't have proper filtering.

I think this is not a real malfunction. Filtering is essential on all circuits.

[MCSpidah]

what is this?

[Coiltec]

Some time ago I have tested it (with ATMega8): Some of them reach 25MHz, others don't. Maybe the AtMega88 goes higher(this chip is rated for 20MHz, the Mega8 only for 16MHz)

[Coiltec]

Perhaps try it with another AVR (of the same type of course). There are manufacturing tolerances. or increase the operating voltage a bit (max. to 6V) if you absolutely need the 25MHz clock.

[agungk]

anyone know the safe margin for everclockin these nifty chips? i can only go up to 20Mhz.

what's the long term effects of overclocking over the chip?

[countryeugene]

Maybe it's because it's built on breadboard and the parasitic capacitance is too high. On a custom PCB and with correct fuse settings it should work OK, at least execute instructions. However, the internal peripherals may not work OK with overclocking.

[HLSDK]

wouldn't you have to change fuses as you change crystals?

[Intosia]

Doesnt they a have a buildin osc?

[truhlikfredy]

but maximal frequency is 16Mhz and it's working coretly on higher frequiencies, but at 25Mhz not. And i think is't working at 25Mhz but then at some random requencies.

[Metalobo]

so you did try like 2 crystal, and the microcontroller fucked up, man, i just dont like atmel.

[calex64]

Atmels are good but that mindless oveclocking kill them...

[ev0lBunny]

uhmm first off it isn't dead it still works as you could see, the point is that it isnt stable at 25 mhz which is either single cycle alu operations failing or maybe the caps used are not of a low enough value , if he used caps that were ment for lets say 8 mhz that will screw the crystal over anytime :)

[truhlikfredy]

exactly