Tuesday, March 12, 2013

How to use the GPIO version of avrdude on the Raspberry Pi

Introduction

I previously showed an implementation of a AVR ISP programmer using the Raspberry Pi GPIO port which can be used to program Atmel's AVR range of microcontrollers with avrdude. An ISP programmer based on this design was incorporated into a shield to interface to the RFM12B radio module. This post explains how to use avrdude to actually program devices.

Software installation

Download the patched version of avrdude from http://project-downloads.drogon.net/files/. I also keep a copy in the RPi_RFM12B_ISP respository, https://github.com/stevemarple/RPi_RFM12B_ISP/tree/master/software/avrdude. You will probably want the armhf (hardware floating-point) version. Download the documentation package for avrdude too. Install the packages using "dpkg -i". For example

sudo dpkg -i avrdude_5.10-4_armhf.deb
sudo dpkg -i avrdude-doc_5.10-4_all.deb

Using avrdude over the GPIO interface is problematic for users other than root. The easiest solution is to give the avrdude binary setgroup permission:
sudo chmod g+s /usr/bin/avrdude

Usage

Selecting the GPIO programmer is simply a matter of including "-P gpio -c gpio" options; the -P option specifies that the GPIO port is used (as opposed to USB, serial or parallel interfaces) whilst the -c option selects the correct programmer type on that port.

For example, to check the signature on an ATmega328P execute the command
avrdude -P gpio -c gpio -p atmega328p

To read the fuses execute the command
avrdude -P gpio -c gpio -p atmega328 -U lfuse:r:-:h -U hfuse:r:-:h -U efuse:r:-:h

Customisation

The packages above define a single programmer called gpio which uses the gpio interface on GPIO pins 8 to 11. Since the RFM12B shield for Raspberry Pi implements two independent programmers I prefer to use gpio0 and gpio1. You can add these by creating a .avrduderc file in your home directory. The file should contain:

programmer
  id    = "gpio0";
  desc  = "Use sysfs interface to bitbang GPIO lines";
  type  = gpio;
  reset = 8;
  sck   = 11;
  mosi  = 10;
  miso  = 9;
;

programmer
  id    = "gpio1";
  desc  = "Use sysfs interface to bitbang GPIO lines";
  type  = gpio;
  reset = 7;
  sck   = 11;
  mosi  = 10;
  miso  = 9;
;

Sunday, March 3, 2013

Three-axis sensor unit for AuroraWatchNet

Three-axis magnetometer sensor unit
Three-axis sensor unit. The RJ-45 connector is for power and I2C data signals, not Ethernet.

AuroraWatchNet is a network of magnetometers for auroral alerts and citizen science. Whilst the  magnetometer is intended to function with one single-axis FLC100 sensor from Stefan-Mayer Instruments I have designed the system to support 3-axis operation by mounting 3 sensor boards at 90° to each other using just standard right-angle PCB connectors. This approach avoids the requirement for external mounting hardware which would be expensive to manufacture.

The power supply (a charge-pump DC-DC converter), temperature sensor and RJ-45 connector are fitted to just one circuit board. It is possible to use only one analogue-to-digital converter (ADC) but given their low cost it was presumed they would be fitted to all boards to enable simultaneous sampling of all 3 axes. The MCP3424 converter was chosen because eight options are available for the I2C address, thus jumpers can be fitted to select a unique address for every ADC on the I2C bus. This converter also features 4 input channels. All magnetometer outputs and the temperature sensor are connected to each ADC so that the spare channels can provide some redundancy in case of an ADC failure. The SYNC connectors of all sensors are linked to synchronise their excitation frequencies.

Several single-axis units have been built and one is in active use by AuroraWatch UK. The photograph above shows the first three-axis unit to be built. Initial testing indicates it functions as intended but the performance of 3 simultaneously-powered sensors in close proximity is yet to be established.