1. Workshop
GPIO I2C SPI
Panic1
woensdag 10 april 2019

2. Installing the Raspberry Pi
NOOBS
NOOBS is an installer that packs a number of RPi ready images, easy to use, but you need an SD card of at least 8Gb to have enough room left for Raspbian
Raspbian
Debian image for Raspbery Pi
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3. Installing NOOBS Format the SD card into one FAT32 partition
Extract the files in the tar ball onto the SD card
Pop the SD card into the RPi and turn it on
Select the image to install and you are ready
Also easy to reinstall an image after it has been messed up, by pressing Shift during startup of the RPi and redo the installation
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4. Installing Raspbian Format the SD card into one FAT32 partition
Use an image writing tool to write the downloaded image to the SD card
Plug the SD card into the RPi and start it up
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5. Documentation on RPi http://www.raspberrypi.org/documentation/
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6. GPIO via command line
> sudo su > echo "22" > /sys/class/gpio/export > echo "out" > /sys/class/gpio/gpio22/direction > echo "1" > /sys/class/gpio/gpio22/value > echo "0" > /sys/class/gpio/gpio22/value > while true; \ > do echo "1" > /sys/class/gpio/gpio22/value; \ > echo "0" > /sys/class/gpio/gpio22/value; \ > done > echo "22" > /sys/class/gpio/unexport Source:
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7. GPIO in a C program
Download and unpack the cross compiler (
Download and unpack Eclipse (
Create new C Project
Executable, Empty Project, Cross GCC
Cross compiler prefix: “arm-bcm2708hardfp-linux-gnueabi-”
Path to cross compiler: ~/workshop\ rasberry\ pi/cross-compiler/tools-master/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin
New source file, copy-paste from
Ctrl-B to Build the project
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8. About the GPIO program
This piece of C code doesn’t use a library, instead it mmaps the device memory, and manipulates the GPIO registers directly
Must be run as root, to activate the root account on Raspbian: sudo passwd
Don’t change the ssh config, make sure the root account stays permitted to login via ssh, we will need this in the later steps when running applications from Eclipse on the RPi target machines
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9. Running the GPIO program
Selec the menu Run
Run configurations
C/C++ Remote Applications
Create a new connection to your RPi board
Don’t forget to generate a ssh key and install it on the RPi
Go to menu Window, Preferences, General, Network Connections, SSH2
If all is well, you can now instruct Eclipse to copy and run the cross compiled program on the target machine
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10. GPIO via CLI, two threads running concurrently on different GPIO pins
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11. I2C background
Source:
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12. I2C by using bcm2835 library
Download to the RPi:
Untar the file, and cd into the folder
./configure
sudo make check
sudo make install
Getting these files into your cross compiler
Copy bcm /src/bcm2835.o and libbcm2835.a from RPi to ~/workshop\ rasberry\ pi/cross-compiler/tools-master/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/arm-bcm2708hardfp-linux-gnueabi/sysroot/lib
You will also need the header file (untar the same tar ball somewhere on your machine locally)
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13. I2C example from bcm2835 lib
We’ll be using the examples provided in the bcm2835 library package
Create a new Eclipse project, same cross compiler settings as before
To be able to use the lib in Eclipse, right click on Project, select Properties, C/C++ General, Paths and Symbols, Libraries tab, add "bcm2835", and in the Includes Tab, add the path to the bcm2835.h file
Copy the i2c.c file into the project, build the project, and run the application like before on the RPi
This time the application won’t work without arguments, try: ./I2cWorkshop -s85 -dw -ib 1 0x01
What are looking at on the scope? Either use the hold function, or put the program in a while(1) loop to see the signal.
Don’t forget to run the application with option –ie to restore the I2C lines back to GPIO at the end
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14. I2C: Trying to write to address 0x55, but no response
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15. SPI background Typical use: Typical use with three slave devices:
Daisy chained with three slave devices:
Source:
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16. SPI via bcm2835 library
Use the example spi.c file from the bcm2835 library package
Same as before, create a new cross gcc project in Eclipse, add the library to the project options, copy the file into the project
Connect the MOSI and the SCLK signals to the scope. The CE0 signal is also interesting
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17. PWM via the bcm2835 library
Use the example pwm.c file from the library package
Same as before
Connect pin 12 (GPIO18) to the scope for the PWM signal
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18. Thank you!
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