Adding software examples

Using wiringPi to demonstrate C applications that access GPIO, SPI and
I2C.

software/gpiotest.cpp

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+/******************************************************************************
+gpiotest.cpp
+Raspberry Pi GPIO demo
+Byron Jacquot @ SparkFun Electronics>
+4/2/2014
+https://github.com/sparkfun/Pi_Wedge
+
+A brief demonstration of GPIO features on the Raspberry Pi, to demonstrate 
+the SparkFun Pi Wedge breakout board.
+
+Resources:
+
+This example makes use of the Wiring Pi library, which streamlines the inteface
+the the I/O pins on the Raspberry Pi, providing an API that is similar to the
+Arduino.  You can learn about installing Wiring Pi here:
+http://wiringpi.com/download-and-install/
+
+The GPIO API is documented here:
+https://projects.drogon.net/raspberry-pi/wiringpi/functions/
+
+WiringPi also installs the very useful command-line utility called 'gpio' 
+which allows you to configure and query pin status.  Check it's man page for 
+more details.
+
+To build this file, I use the command:
+>  g++ gpiotest.cpp -lwiringPi
+
+Then to run it, I have to use sudo, as it creates restricted file resources.
+> sudo ./a.out
+
+WiringPi defines its own pin numbers, in a contiguous range, from 0 to 16.  
+These numbers account for the V1/V2 hardware differences.  You can alternately 
+use the RPi/Broadcom pin numbers.
+
+This test will repurpose the UART pins.  If you're using a terminal on the UART, 
+constrain it to pins 0 through 14.  If you're using SSH/telnet, you can include 
+pins 15 and 16.
+
+Development environment specifics:
+Tested on Raspberry Pi V2 hardware, running Raspbian.
+Building with GCC 4.6.3 (Debian 4.6.3-14+rpi1)
+
+This code is beerware; if you see me (or any other SparkFun employee) at the
+local, and you've found our code helpful, please buy us a round!
+
+Distributed as-is; no warranty is given.
+******************************************************************************/
+
+#include <iostream>
+#include <errno.h>
+#include <wiringPi.h>
+
+using namespace std;
+
+// This will only touch 0 through 14.  15 and 16 are the UART, which we 
+// wouldn't want to reconfigure is you're using them for a terminal.
+// If you're using SSH, you can run up to 16.
+static const int MAX_PIN = 14;
+
+int main()
+{
+   int result;
+
+   // Init using the wiring Pi numbering scheme ( GPIOs referenced as
+   // a contiguous 0 through 16 range).
+   //
+   // Could alternately call:
+   // - wiringPiSetupGpio() to use the native Pi pin numbers
+   // - wiringPiSetupSys() to use pre-exported /sys/class/gpio pins.  This
+   //                      requires that the pins be pre-exported, but doesn't 
+   //                      require root access to run the application.
+   result = wiringPiSetup();
+
+   // Result of -1 indicates error
+   cout << "Setup result: " << result << endl;
+
+   // set all pins as outputs
+   for(int i = 0; i <= MAX_PIN; i++)
+   {
+      pinMode(i, OUTPUT);
+
+      cout << "init'd pin: " << i << endl;
+   }
+
+   // Cycle through the pins, setting one at a time high.
+   // Repeat 10 times.
+   // This allows us to check them with a meter or oscilloscope.
+   for(int i = 0; i < MAX_PIN; i++)
+   {
+      for(int j = 0; j <= MAX_PIN; j++)
+      {
+         if( (i % 17) == j)
+         {
+            cout << "Pin " << j << " set high." <<endl;
+            digitalWrite(j, HIGH);
+         }
+         else
+         {
+            digitalWrite(j, LOW);
+         }
+      }
+
+      sleep(1);
+   }
+}

software/i2ctest.cpp

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+/******************************************************************************
+i2ctest.cpp
+Raspberry Pi I2C interface demo
+Byron Jacquot @ SparkFun Electronics>
+4/2/2014
+https://github.com/sparkfun/Pi_Wedge
+
+A brief demonstration of the Raspberry Pi I2C interface, using the SparkFun
+Pi Wedge breakout board.
+
+Resources:
+
+This example makes use of the Wiring Pi library, which streamlines the inteface
+the the I/O pins on the Raspberry Pi, providing an API that is similar to the
+Arduino.  You can learn about installing Wiring Pi here:
+http://wiringpi.com/download-and-install/
+
+The I2C API is documented here:
+https://projects.drogon.net/raspberry-pi/wiringpi/i2c-library/
+
+The init call returns a standard file descriptor.  More detailed configuration
+of the interface can be performed using ioctl calls on that descriptor.
+See the wiringPi I2C implementation (wiringPi/wiringPiI2C.c) for some examples.
+Parameters configurable with ioctl are documented here:
+http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/i2c/dev-interface
+
+Hardware connections:
+
+This file interfaces with the SparkFun MCP4725 breakout board:
+https://www.sparkfun.com/products/8736
+
+The board was connected as follows:
+(Raspberry Pi)(MCP4725)
+GND  -> GND
+3.3V -> Vcc
+SCL  -> SCL
+SDA  -> SDA
+
+An oscilloscope probe was connected to the analog output pin of the MCP4725.
+
+To build this file, I use the command:
+>  g++ i2ctest.cpp -lwiringPi
+
+Then to run it, first the I2C kernel module needs to be loaded.  This can be 
+done using the GPIO utility.
+> gpio load i2c 400
+> ./a.out
+
+This will run the MCP through it's output range several times.  A rising 
+sawtooth will be seen on the analog output.
+
+Development environment specifics:
+Tested on Raspberry Pi V2 hardware, running Raspbian.
+Building with GCC 4.6.3 (Debian 4.6.3-14+rpi1)
+
+This code is beerware; if you see me (or any other SparkFun employee) at the
+local, and you've found our code helpful, please buy us a round!
+
+Distributed as-is; no warranty is given.
+******************************************************************************/
+
+#include <iostream>
+#include <errno.h>
+#include <wiringPiI2C.h>
+
+using namespace std;
+
+int main()
+{
+   int fd, result;
+
+   // Initialize the interface by giving it an external device ID.
+   // The MCP4725 defaults to address 0x60.   
+   //
+   // It returns a standard file descriptor.
+   // 
+   fd = wiringPiI2CSetup(0x60);
+
+   cout << "Init result: "<< fd << endl;
+
+   for(int i = 0; i < 0x0000ffff; i++)
+   {
+      // I tried using the "fast write" command, but couldn't get it to work.  
+      // It's not entirely obvious what's happening behind the scenes as
+      // regards to endianness or length of data sent.  I think it's only 
+      // sending one byte, when we really need two.
+      //
+      // So instead I'm doing a 16 bit register access.  It appears to 
+      // properly handle the endianness, and the length is specified by the 
+      // call.  The only question was the register address, which is the 
+      // concatenation of the command (010x = write DAC output) 
+      // and power down (x00x = power up) bits.
+      result = wiringPiI2CWriteReg16(fd, 0x40, (i & 0xfff) );
+
+      if(result == -1)
+      {
+         cout << "Error.  Errno is: " << errno << endl;
+      }
+   }
+}

software/spitest.cpp

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+/******************************************************************************
+i2ctest.cpp
+Raspberry Pi I2C interface demo
+Byron Jacquot @ SparkFun Electronics>
+4/2/2014
+https://github.com/sparkfun/Pi_Wedge
+
+A brief demonstration of the Raspberry Pi I2C interface, using the SparkFun
+Pi Wedge breakout board.
+
+Resources:
+
+This example makes use of the Wiring Pi library, which streamlines the inteface
+the the I/O pins on the Raspberry Pi, providing an API that is similar to the
+Arduino.  You can learn about installing Wiring Pi here:
+http://wiringpi.com/download-and-install/
+
+The wiringPi SPI API is documented here:
+https://projects.drogon.net/raspberry-pi/wiringpi/spi-library/
+
+The init call returns a standard file descriptor.  More detailed configuration
+of the interface can be performed using ioctl calls on that descriptor.
+See the wiringPi SPI implementation (wiringPi/wiringPiSPI.c) for some examples.
+Parameters configurable with ioctl are documented here:
+http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/spi/spidev
+
+
+Hardware connections:
+
+This file interfaces with the SparkFun Serial 7 Segment display:
+https://www.sparkfun.com/products/11629
+
+The board was connected as follows:
+(Raspberry Pi)(Serial 7 Segment)
+GND  -> GND
+3.3V -> Vcc
+CE1  -> SS (Shift Select)
+SCK  -> SCK 
+MOSI -> SDI
+MISO -> SDO
+
+To build this file, I use the command:
+>  g++ spitest.cpp -lwiringPi
+
+Then to run it, first the spi kernel module needs to be loaded.  This can be 
+done using the GPIO utility.
+> gpio load spi
+> ./a.out
+
+This test uses the single-segment mode of the 7 segment display.  It shifts a 
+bit through the display characters, lighting a single character of each at a 
+time.
+
+Development environment specifics:
+Tested on Raspberry Pi V2 hardware, running Raspbian.
+Building with GCC 4.6.3 (Debian 4.6.3-14+rpi1)
+
+This code is beerware; if you see me (or any other SparkFun employee) at the
+local, and you've found our code helpful, please buy us a round!
+
+Distributed as-is; no warranty is given.
+******************************************************************************/
+
+#include <iostream>
+#include <errno.h>
+#include <wiringPiSPI.h>
+
+using namespace std;
+
+// channel is the wiringPi name for the chip select (or chip enable) pin.
+// Set this to 0 or 1, depending on how it's connected.
+static const int CHANNEL = 1;
+
+int main()
+{
+   int fd, result;
+   unsigned char buffer[100];
+
+   cout << "Initializing" << endl ;
+
+   // Configure the interface.
+   // CHANNEL insicates chip select,
+   // 500000 indicates bus speed.
+   fd = wiringPiSPISetup(CHANNEL, 500000);
+
+   cout << "Init result: " << fd << endl;
+
+   // clear display
+   buffer[0] = 0x76;
+   wiringPiSPIDataRW(CHANNEL, buffer, 1);
+
+   sleep(5);
+
+   // Do a one-hot bit selection for each field of the display
+   for(int i = 1; i <= 0x7f; i <<= 1)
+   {
+      // the decimals, colon and apostrophe dots
+      buffer[0] = 0x77;
+      buffer[1] = i;
+      result = wiringPiSPIDataRW(CHANNEL, buffer, 2);
+
+      // The first character
+      buffer[0] = 0x7b;
+      buffer[1] = i;
+      result = wiringPiSPIDataRW(CHANNEL, buffer, 2);
+
+      // The second character
+      buffer[0] = 0x7c;
+      buffer[1] = i;
+      result = wiringPiSPIDataRW(CHANNEL, buffer, 2);
+
+      // The third character
+      buffer[0] = 0x7d;
+      buffer[1] = i;
+      result = wiringPiSPIDataRW(CHANNEL, buffer, 2);
+
+      // The last character
+      buffer[0] = 0x7e;
+      buffer[1] = i;
+      result = wiringPiSPIDataRW(CHANNEL, buffer, 2);
+
+      // Pause so we can see them
+      sleep(5);
+   }
+
+   // clear display again
+   buffer[0] = 0x76;
+   wiringPiSPIDataRW(CHANNEL, buffer, 1);
+
+}