malfunction of atmel avr mega overclocked at 25mhz

malfunction of atmel avr mega overclocked at 25mhz.

0:00-0:35 = clocked at 25Mhz not working corectly
0:35-0:49 = working corectly at 25Mhz
1:05-1:23 = original frequency

Category:

Howto & Style

Tags:

• malfunction
• of
• atmel
• avr
• mega
• overclocked
• at
• 25mhz

[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

[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

[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?

[amazingrapist]

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

[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.

[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.

[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.