How do I set the clock speed fuses on an ATtiny85 when using an Arduino as a programmer?

Question

I'm following this tutorial, programming the ATtiny85 with an Arduino, using it to play some tones (through a piezo speaker). I'm struggling with getting the tones at the right pitch (I'm creating the wave forms manually, as the tone() function is unsupported on the ATtiny85).

I believe the problem may be down to differing clock speeds on the Arduino and ATtiny. I understand the clock speed can be altered on the ATtiny, how do I accomplish this using the arduino environment?

Answer 1

I believe the Arduino software (libraries and all) assumes you are operating at 16MHz. If you apply that assumption to the clock you are actually running at... things should work out. Assuming you are running the Tiny85 on it's internal oscillator I think it runs at 1MHz, so just multiply all your delay statements (and other notions of time) by 16.

If you need better accuracy than the internal oscillator provides you should think about using an external crystal or a resonator, but you will need to change the fuse settings of the AVR for that to work, and I think you will need a programmer like the AVRISP mkII to do that with AVR Studio (my recommendation).

I don't know much about the ArduinoISP sketch but to me it looks like it bit bangs the ISP protocol to upload a program to the target chip (not the on board Mega328), not sure it is equipped to manipulate fuses. ArduinoISP is documented here http://arduino.cc/en/Tutorial/ArduinoISP, fwiw. Note that you can't use a UNO currently to run the ArduinoISP sketch. It doesn't look to me like you can use the sketch to make the Arduino a viable interface for using the AVR Studio GUI tools.

Answer 2

It appears you are using ArduinoISP, try using AVR Studio or the command line options for avrdude. Depending on how the ArduinoISP was written, it may function just like an Atmel AVRISP mkII or similar.

Answer 3

I think you can set the fuses with the ArduinoISP, but not with the Arduino IDE but with avrdude, check this link. Never tested it myself.

The tutorial explicitly says you can use the Arduino UNO and I have tested it and worked, so I can confirm that, so the ArduinoISP page is outdated and the UNO warning should be ignored. If your UNO was one from the first batch you probably have a faulty bootloader, you will need to reflash the bootloader. Check this page for more information (ignore the serial numbers, all my UNOs were not from that series and had problems).

The ported core libraries you downloaded from the tutorial are written to use the 1MHz internal oscillator (confirmed from boards.txt file), so maybe the timming problem might be in the ported core libraries or in your code.

Kind regards

Answer 4

Default fuse settings for the ATtiny85 are: lfuse 0x62, hfuse 0xdf, efuse 0xff. This uses the internal RC (8 MHz) oscillator with "divide by 8" so clock is 1 MHz.

See http://www.engbedded.com/fusecalc for more fuse settings.

You can still use avrdude directly to change fuse settings of your ATtiny85 even when using an ArduinoISP as the programmer.

If you do end up manually changing fuse to alter the clock, be sure to edit the attiny85.build.f_cpu line of your [arduino_folder]\hardware\attiny45_85\boards.txt file.

Answer 5

I'm using Arduino UNO + ArduinoISP successfully.

Add -U flags to your avrdude command to set any or all of the three ATtiny fuses.

avrdude -p attiny85 -P com8 -c stk500v1 -b 19200 -U lfuse:w:0x6f:m -U flash:w:main.hex

The clock selection is done in bits[3:0] on the third fuse ('Fuse Low Byte'). Set them as follows to make use of an external crystal (of 8MHz or faster):

-U lfuse:w:0x6f:m

Its definition (I infer) must be something like: [Fuse Low Byte]:[write]:[hex value]:[set manually]

The default value for the four high bits of this byte are 0110, so leave the 6 in 0x6f as it is, and only change the second digit, the f (its default value is 2).

NB: If your processes take longer or shorter than you expect, check your clock prescaler and your definition of F_ CPU.

Answer 6

Try using the related tutorial by the same group (MIT's High-Low Tech) entitled Programming an ATtiny w/ Arduino 1.0.

A quick summary: From the Tools-> Board menu in the Arduino IDE, select the ATtiny85 and the frequency you wish to run at (1 or 8 Mhz internal clock, or 20Mhz external crystal) and then use the Tools -> Burn Bootloader". I believe selecting the desired speed board modifies the way the delay() and other time-related Arduino functions work in order to sync up with the clock speed.

I have had success with this approach myself using some ATtiny84 chips. The simple blink program is fixed, as well as more sensitive timing required for manually controlling pulses sent to a servo using delayMicroseconds().