Monthly Archives: May 2010

Freetronics 2010 (Arduino Duemilanova) Overclocking & Review

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Recently, I picked up a Freetronics 2010 from Little Bird Electronics.

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I thought that it would make a nice upgrade to my Dogbot test bed. It uses the same USB connector as Dogbot’s Pololu SVP, so it saves me from keeping different USB cables handy, but is in every way 100% the same as the Arduino Duemilanove that I’ve been using up to now.

But, everything I own is hacked in some way. So as usual, I thought that the 2010 could be improved, just as I’ve improved the Duemilanove before it, by overclocking it to 22.1184MHz.

Overclocking to 22.1184MHz

So why change the clock frequency to this odd number of 22.1184MHZ, and not to 20MHz which would be in specification?

It turns out that because of the binary and integer world the 2010 and the Duemilanova ATmega328p MCU live in, it is much better have a “nice” binary and integer friendly base frequency. Unfortunately, although 16MHz on a 2010 or Arduino sounds nice, from the point of view of integer programming, clock scaling, and UART interfacing, it is difficult to get clean integer numbers.

A small example.
16MHz clock scaled to 115200baud = 138.888888889 so rounding gives an error term.
20MHz clock scaled to 115200baud = 173.6111111111 so, again, rounding gives an error term.
22.1184MHz clock scaled to 115200baud = 192 with no rounding error.

Also, even though we are getting 16,000,000 instructions per second out of a standard?2010, and that should be enough for any application. I can get 22,118,400 or a 38% improvement for the cost of a few cents. So, why wouldn’t you?

What kind of issues can occur?

Well, over-clocking means that the ATmega328p is out of specification. But, I’m not too worried about pushing specification on this project, as the 328p is certified for an industrial operating temperature range, which is way outside of my operating temperature… There are also unverified reports of AVR ATmegas working successfully up to 32MHz.

In the overall scheme of things, raising the clock frequency on the AVR ATmega328p above specification by 10% to 22.1184MHz is no big deal.

Upgrading Process

1. Obtain a 22.1184MHz HC49/US crystal from Digikey They’re pretty cheap. Buy a bag in case of accidents.

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2. Use a knife tip under the existing 16MHz crystal to give you a lever to pressure it into removal, without burning your fingers. It will get very hot!

3. Turn over the board and use a soldering iron to heat the joints, whilst leaning on the knife to lever out the 16MHz crystal. Once it is removed, use some solder wick or similar to remove excess solder, and make it easier to insert and solder the new 22.1184MHz crystal.

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4. Building a new bootloader. In replacing the crystal, the 2010 is effectively bricked. You can no longer communicate with it using the standard bootloader. It is now running too fast and out of specification for avrdude to communicate with it, so we have to compile and burn a new boot loader before we go any further. I choose to use the Adaboot328 bootloader from Ladyada. It resolves a few known issues with Arduino compatible boards, and is easy to compile.

In the ATmegaBOOT_xx8.c file, change the UART baud rate to 115200, if you use avrdude for programming (if using Arduino IDE, do not change this from 19200). Who has time to wait around these days for 19200 baud, anyway?

/* set the UART baud rate */
#define BAUD_RATE?? 115200

In the Makefile, change the AVR_FREQ value to 22118400L for the adaboot328: TARGET.

adaboot328: TARGET = adaboot328
# Change clock frequency from 16000000L
adaboot328: AVR_FREQ = 22118400L

Then, compile the bootloader, and keep it safe.

5. Prepare an ISP. There are many alternative ways to do this, and here is not the place to describe the alternatives. Suffice to say that I used the AVRISP method in the Arduino-0018 IDE. I’ve struggled with avrdude (which I otherwise use for everything) as a bootloader ISP. I don’t know why, but I can’t make it work.

It happens that I have a standard Arduino clone available, which I prepare as the AVRISP, by uploading the following sketch File>Examples>ArduinoISP.

6. To be able to use Arduino IDE to burn our special bootloader, you have to replace the standard ATmegaBOOT_168_atmega328.hex bootloader file, found in ~arduino/bootloaders/atmega/ with our newly generated file. And, to make things simple, I just rename or remove the standard one, and replace it with our newly prepared and renamed bootloader with this name
ATmegaBOOT_168_atmega328.hex.

7. Connect our Freetronics 2010 up using the AVRISP connections, described on the Arduino web site. Make sure we have the right board type selected; it should be Duemilanova w/ ATmega328. Then using the Arduino IDE use Tools > Burn Bootloader > w/ Arduino as ISP.

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8. Program a sketch using either the Arduino IDE, or using avrdude, remembering that the baudrate is set to 115200. And, enjoy.

Conclusions regarding the Freetronics 2010.

Its a very well designed and produced device, that is 100% compatible with the Arduino Duemilanova. Some advantages are: the mounting holes are slightly larger so cable ties go through nicely, smaller USB connector is more common than the B connector used on Duemilanova, and there’s no solder in the holes for the X3 connector so it is easy to add headers to make it possible to burn its own bootloader (if you want).

It runs my freeRTOS build with no problems, as seen in this demo on my Dogbot test bed with a Robot Electronics Thermopile, and Sharp IR Distance sensor.

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DogBot – Post 5

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So some time has passed and I’ve had some success with different aspects of my robot.

For simplicity, I’m using a test bed based on an Arduino Duemilianova connected to a Nerdkits sourced display. I’ve hooked the display up as if it was a Pololu Orangutan SV-328 and am using Pololu libraries to write to it. Also, I’ve been working on the actual SVP based robot, so both of which are working well.

The processor 328p is used for the Duemilianova and requires the use of the Timer0, which implies no Pololu motor library code is possible without conflicts. However this is not an issue, as the Duemilianova doesn’t have motor drives anyway. The actual DogBot has the 1284p which is used in the SVP and uses Timer3, which has no limitations on any known libraries to my knowledge.

The freeRTOS code is posted on the Pololu Forum, mostly just back-up as the application code is very immature.

At  this stage I’ve got all of the I2C bus based sensors working, based on code developed by Fleury. So, I can read the thermal sensor for its 8 pixels, and equally importantly, I can read the SRT10 Ultrasonic Sensor for distance in cm. One issue with the ultrasonic sensor is that its field of vision is so great that it basically detects anything “in front” of it. Good to not run into things, but pretty useless as a fine directional capability. It seems lucky that the Sharp IR distance sensors are very directional, and sufficiently accurate as a complement. The analog sensor readings are working well too, though I still have to create a ADC to cm regression.

From the point of view of sensing, it looks like the Sharp IR sensors will be the reference. With the SRT10 sonar being most relevant to create a “zone of safety” where I can be assured that the nearest object in a cone of 120deg is measured, but can’t be sure exactly which direction the object is. On the thermal side, I will get a vector (direction and temperature) from the sensing location, but no distance. But, that I knew and expected.

Putting some effort into designing the motor control, or Transport Task, has taken up my thoughts recently. I don’t want to link the odometry available from the quadrature encoders back into the mapping or routing task. Similarly, I don’t want to link the intertial navigation available from yaw and linear acceleration sensors into the motor task.

I think the transport task should simply take a vector,  relative to the the current pose of the robot, and execute these translation commands subject to feedback from odometry, leaving the inertial navigation to another task.

This fits well into the design of the hardware, as odometry can can be queried from the Pololu SVP ancillary processor, without blocking, and the motor PWM drivers can be also managed without blocking other tasks. This creates a self contained task that does not need to share resources with other tasks.

However, the inertial sensors are analogue readings and the ADC will need to be shared with the Sharp IR distances sensors. Creating the need for a semaphore, and blocking based on the availability of the ADC.

Because of the battery issues described in Post 4, I’ve had to remove the servo neck of the DogBot. Therefore, I will implement the option for motion to be along circular paths, as well as along a straight line. Motion along a straight line, with stationary rotations to create the correct pose prior to departure, are the best paths to arrive at the destination with the lowest risk and shortest path. However, with a fixed sensor head, straight lines don’t fill the map with information as they leave the sensors always pointing in the same direction.

If the DogBot proceeds from A to B via a circular route (if this is requested by the mapping or logistics task), then the sensors will be pointed at all directions from +90 to -90 degrees along the path to the destination. Allowing the travel time to be used effectively for data acquisition.

If I’m feeling smart, then I can create any number of route subdivisions, and force DogBot to describe a path of smooth semicircles to the destination, gathering sensor data along the route.

The inertial sensors can be run in a parallel task (using the ADC along with the Sharp IR sensors), with the odometry (from the ancillary processor) to cross check that the expected distances and directions are traveled. Whilst I think the odometry is more likely to be accurate, the map will be updated constantly so some inaccuracy should be expected and tolerated by the code.

My next step is to design this transport task. This task should take distance, bearing and path description (straight line, circle, sinusoidal, etc) and carry it out to the best of its ability (odometry PID data only). I expect resolving this effort will take the next few weeks, and perhaps longer.

Later work is to develop the logistics and routing task that will issue the navigation requests to the transport task.

Continued with Post 6 (one year later).