Atmega328P @ 11,0592MHz

Other Hardware 3rd Party Boards
1

Hi,

for my current project, I built my own circuit for the Atmega328 taken from the Arduino UNO.
It runs at 3,3V.
Since the maximum rating for the µC @ 3,3V is about 13MHz, I have to use another oscillator.
Since I want to transmit data at 115200baud, I do not want to use 8MHz, since the mistake rate is quite high.
Instead, I chose 11,0592MHz.
As a result, I will have to manipulate the bootloader in order to make it work correctly.
Did anyone of you already do this or does anyone of you how exactly I have to do this?

Thanks for your help!

2

I will have to manipulate the bootloader in order to make it work correctly.
Did anyone of you already do this or does anyone of you how exactly I have to do this?

Well, you COULD upload while the 328 is in the Arduino running at 16MHz, and then move it into your 11MHz target system; no bootloader changes would be required.

What host system are you using (windows, mac, linux), and do you have AVR tools installed other than Arduino? (such as WINAVR or CROSSPACK-AVR)

In theory, you modify the makefile in the hardware/arduino/bootloaders/optiboot directory so that you have a target that has AVR_FREQ = 11059200 and compile that target, but with the current distributions you need an AVR development environment installed in order to do the build.

3

Thanks for your response.

Well my problem is that the baud-rate of the Atmega is relative to the clock speed-so when I choose a lower clock speed, the serial communication will get messed up.
I have AVR Studio installed on my Windows 7 PC, which I guess would do the job.
I tried to change the makefile and recompile it, I did not really know how to proceed and was thereful not successful.
So how exactly do I have to do this?

4

you open the make file in your text editor and you need to change this settings

# enter the parameters for the avrdude isp tool
ISPTOOL	   = usbasp
ISPPORT	   = usb
ISPSPEED   =

depending on the programmer your using if you use arduino as isp should look like this

# enter the parameters for the avrdude isp tool
ISPTOOL	   = stk500
ISPPORT	   = \\.\COMx #where x its the number of the serial port assigned by windows to your arduino 
ISPSPEED   =  -b19200

after that you need to edit this

atmega328: AVR_FREQ = 16000000L

to

atmega328: AVR_FREQ = 11059200L

and save the file

open command line change directory to where you have the optiboot and type

make atmega328

this will make the .hex file and

make atmega328_isp

hope this helps

5

Thanks for this answer thats exactly what I needed:)

I got two more questions:

  1. Does anybody know the ISP settings for the AT AVR ISP2 USB-programmer?
    If not, which programmer can you recommend me?

  2. I took a look at the schematic of the Duemilanove board, and it seems like the FTDI chip does not use an oscillator...so could I just change the oscillator for the atmega328 to 11,0592MHz after I burnt the new bootloader, and will I be able to communicate with/program the µC via the FTDI chip then?

Thanks!

6

according to avrdude its stk500v2
yes you can change the crystal and and everything should run smooth

7

The FTDI chip uses it's own internal oscillator. It will be happy so long as the atmega328 is talking at a correct baud-rate.

BTW, with Westfw's improved version of Optiboot it's very easy to recompile the bootloader. Only the Adruino IDE is needed. Take a look at https://github.com/WestfW/Arduino/tree/master/hardware/arduino/bootloaders/optiboot

I just tried a compilation with "AVR_FREQ = 11059200L". Although I don't have an 11MHz crystal handy, it does appear that the bootloader sets the baud-rate generator clock correctly.

8

The odds are excellent that the 328 will run 16MHz at 3.3v, every jeenode in existence does this, and I've run half a dozen chips at 3.3v and 16MHz will excellent results.

9

Do you actually need the bootloader? When I migrate prototypes from the Arduino to dedicated hardware, I program them via ICSP instead.

10

Well the problem is that I have to take some really fast and precise mesurements, and as I use a two XBee radios to communicate with the PC, I'm limited to 115200 baud.
At 16 MHz, the mistake rate for the serial communication at 115200 baud is about 3,5%, which is two much for my application since I have to calculate integreals from the values. (I use a gyroscope as well as an accelerometer.)

The problem is that I'm currently still prototyping, and the external components used all run at 3,3V, which unfortunately means that I have to swap the µC between the circuit and the arduino board to program it, which also means I need to use the bootloader.

Thanks for your help everyone, I didn't get WestfW's optimised optiboot to work yet, but I'm working on it, and hopefully I will soon get my ISP programmer back so I can proceed.

11

Btw, why is the optimised optiboot easier to manipulate?

12

Bill has improved the makefile so that it's easier to compile, buy adding the paths to the compiler and other tools and translating forward-slashes into back-slashes where necessary. There are also some bug-fixes and improvements to the code.

Download the source files from Github, put them in the bootloaders directory in the IDE (eg. C:\Users\Tim\Documents\Arduino\ide\v10r1\hardware\arduino\bootloaders\optiboot_v44), and run omake.bat. That's all there is to it.