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--- chumbyhackerboard:i2c [2010/08/28 21:37]
ladyada created
+++ chumbyhackerboard:i2c [2010/09/02 20:29]
binkl Change address 58 to 29 so that the wiki text matches the i2cfail.gif
@@ Line 1: / Line 1: @@
-**THIS TUTORIAL IS STILL IN PROGRESS**
+====== i2c twiddler ======
-====== i2c ======
 First, you'll need to have a toolchain installed so make sure you go back and install it!
-Next, scroll down and copy the i2c C code board. Open up your terminal to the CHB and type in **mkdir /mnt/storage/dev; cd /mnt/storage/dev; cat > i2c.c** into the terminal and hit return.
+Sean Cross wrote a great i2c twiddler-tool. This allows you to poke and peek at i2c chips right from the command line. Nice!
+Scroll down and copy his i2c C code. Open up your terminal to the CHB and type in **mkdir /mnt/storage/dev** (or whatever place you want to store your code), then **cd /mnt/storage/dev** and finally **cat > i2c.c** into the terminal and hit return.
 Then paste in the code and finish by typing **Control-D**
@@ Line 13: / Line 13: @@
 {{:chumbyhackerboard:i2ccompile.gif|}}
+====== Reading the MMA7455L accelerometer ======
+There's a Freescale +-2G to +-8G 3-access accelerometer on the CHB for you to play with, lets get some readings. First off, we need to know what the i2c address is. [[http://www.freescale.com/files/sensors/doc/data_sheet/MMA7455L.pdf|Open up the datasheet]] and look for the section called "i2c Slave Address"
+{{:chumbyhackerboard:mma7455addr.gif|}}
+**$1D** means hexadecimal 0x1D which is the same as decimal 29. Great! Lets read byte #0 from the accelerometer by typing in **./i2c r 29 0**
+{{:chumbyhackerboard:i2cfail.gif|}}
+?? We got an error that the register was not readable. This means the chip could not be found on the i2c bus. :( But then we rememer that i2c addresses are 7 bits long and are transmitted in the upper bits of an 8-bit byte. So we actually need to shift the address up by 1 bit. That's easy to do, though, just multiply by 2 to get i2c address **58**
+{{:chumbyhackerboard:i2cok.gif|}}
+Rock! Now we need to figure out what registers we can read, looking at the datasheet we see:
+{{:chumbyhackerboard:mma7455reg.gif|}}
+There's a lot of stuff! Lets start with one we know is going to work, like **$0D** (hex 0x0D = dec 13)
+{{:chumbyhackerboard:mmareg13.gif|}}
+It in fact returns the value 0x1D which we know is the i2c address
+====== Acceleromate! ======
+OK so now we want to get that XYZ data, right? Looking at the register file it seems like the first 6 bytes are used for 10-bit readings, but we can get single 8 bit readings from registers number 6, 7 and 8
+If you're careful you can read those registers while having a friend gently shake the board, you'll see different values returned
+{{:chumbyhackerboard:mmai2ctest.gif|}}
+However, wouldn't it be great if you didn't need a friend to shake the board while you pressed Up-arrow & Return? Lets edit Sean's code. To begin we will put **#define**'s in for the address and registers
+<code>
+// The 'raw' 7 bit address shifted up
+#define MMA7455_I2CADDR (0x1D * 2)
+// The registers to read!
+#define MMA7455_XOUT8 6
+#define MMA7455_YOUT8 7
+#define MMA7455_ZOUT8 8
+</code>
+Then replace the **main()** function with our own which is shorter and only reads those registers to print out the values
+<code>
+int main(int argc, char **argv) {
+    int i2c_file;
+    int8_t x, y, z;  // the readings are 8 bits and signed!
+    // Open a connection to the I2C userspace control file.
+    if ((i2c_file = open(I2C_FILE_NAME, O_RDWR)) < 0) {
+        perror("Unable to open i2c control file");
+        exit(1);
+    }
+    // ignore arguments!
+    while (1) {
+      // read X and Y and Z from the register
+      if( get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_XOUT8, &x) ||
+	  get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_YOUT8, &y) ||
+	  get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_ZOUT8, &z) ) {
+	printf("Unable to read register!\n");
+	return -1;
+      }
+      printf("X = %d\tY = %d\tZ = %d\n", x, y, z);
+    }
+    close(i2c_file);
+    return 0;
+}
+</code>
+Note the while() loop, and that we read all three registers and stick the results into 8-bit signed variables. Then we printf() 'em all and loop again.
+You can grab all of the code below
+Stick the code in a new file called **mma7455.c** by copying and pasting as before. Then compile by running **gcc -o mma7455 mma7455.c** and run with **./mma7455**.  Now shake it!
+{{:chumbyhackerboard:shaken.gif|}}
+There you go! Now you can talk to the accelerometer to get motion data, and this code is easily adaptable for any i2c chip you may want to use. Enjoy!
-====== Code ======
+====== Basic i2c twiddler Code ======
 <file>
@@ Line 187: / Line 275: @@
+    return 0;
+}
+</file>
+====== MMA7455L reader ======
+<file>
+/*
+ This software uses a BSD license.
+Copyright (c) 2010, Sean Cross / chumby industries &  Limor Fried / adafruit industries (we are both industrious people, eh?)
+All rights reserved.
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions
+ are met:
+ * Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in the
+   documentation and/or other materials provided with the
+   distribution.
+ * Neither the name of Sean Cross / chumby industries nor the names
+   of its contributors may be used to endorse or promote products
+   derived from this software without specific prior written
+   permission.
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ POSSIBILITY OF SUCH DAMAGE.
+ */
+#include <stdio.h>
+#include <linux/i2c.h>
+#include <linux/i2c-dev.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <string.h>
+// The 'raw' 7 bit address shifted up
+#define MMA7455_I2CADDR (0x1D * 2)
+// The registers to read!
+#define MMA7455_XOUT8 6
+#define MMA7455_YOUT8 7
+#define MMA7455_ZOUT8 8
+#define I2C_FILE_NAME "/dev/i2c-0"
+static int get_i2c_register(int file,
+                            unsigned char addr,
+                            unsigned char reg,
+                            unsigned char *val) {
+    unsigned char inbuf, outbuf;
+    struct i2c_rdwr_ioctl_data packets;
+    struct i2c_msg messages[2];
+    /*
+     * In order to read a register, we first do a "dummy write" by writing
+     * 0 bytes to the register we want to read from.  This is similar to
+     * the packet in set_i2c_register, except it's 1 byte rather than 2.
+     */
+    outbuf = reg;
+    messages[0].addr  = addr;
+    messages[0].flags = 0;
+    messages[0].len   = sizeof(outbuf);
+    messages[0].buf   = &outbuf;
+    /* The data will get returned in this structure */
+    messages[1].addr  = addr;
+    messages[1].flags = I2C_M_RD/* | I2C_M_NOSTART*/;
+    messages[1].len   = sizeof(inbuf);
+    messages[1].buf   = &inbuf;
+    /* Send the request to the kernel and get the result back */
+    packets.msgs      = messages;
+    packets.nmsgs     = 2;
+    if(ioctl(file, I2C_RDWR, &packets) < 0) {
+        perror("Unable to send data");
+        return 1;
+    }
+    *val = inbuf;
+    return 0;
+}
+int main(int argc, char **argv) {
+    int i2c_file;
+    int8_t x, y, z;  // the readings are 8 bits and signed!
+    // Open a connection to the I2C userspace control file.
+    if ((i2c_file = open(I2C_FILE_NAME, O_RDWR)) < 0) {
+        perror("Unable to open i2c control file");
+        exit(1);
+    }
+    // ignore arguments!
+    while (1) {
+      // read X and Y and Z from the register
+      if( get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_XOUT8, &x) ||
+	  get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_YOUT8, &y) ||
+	  get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_ZOUT8, &z) ) {
+	printf("Unable to read register!\n");
+	return -1;
+      }
+      printf("X = %d\tY = %d\tZ = %d\n", x, y, z);
+    }
+    close(i2c_file);
     return 0;
 }
 </file>

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