Example i2c test

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This is a guide to the i2c_test example project included in the EMAC OE SDK.

I²C is a two wire serial interface used to connect to a variety of sensor and I/O devices. The interface uses only two bi-directional open-drain I/Os, Serial Data Line (SDA) and Serial Clock (SCL), to communicate to devices based on an address encoded within the data transmission. SDA is a data signal which sends and receives serially transmitted data. SCL is a clock signal which is used to determine when to latch data from the SDA line.

This procedure provides an overview of how to compile and run the i2c_test C example project. This is an example test interface for reading/writing to the Linux I²C device interface. It is only relevant if the I²C device interface is enabled and an external I²C device is connected to the bus. It assumes familiarity with the C programming language and is intended to be used by experienced programmers who are looking to learn the EMAC SDK.

For more information about the protocol see the following page: http://en.wikipedia.org/wiki/I²C

The i2c_test project builds one executable: i2c_test.

Opening, Building, and Uploading the Project Files

For information on opening the project from within Eclipse, please see, Importing the EMAC OE SDK Projects with Eclipse. Then, follow Using the EMAC OE SDK Projects with Eclipse for information on how to build, upload, and execute the example.

Alternatively, the Makefile can be used with the make command from the command-line to build and upload the example. For more information on this method, please see, Using EMAC OE SDK Example Projects.

Usage and Behavior

Hardware Requirements

The i2c_test C example project will run on any EMAC carrier board which has an I²C interface (see also the EMAC I²C Programming page).

Using i2c_test

The i2c_test program is executed from the console. It takes no parameters.

root@emac-oe~:$ ./i2c_test

A menu will appear in the terminal:

Select a function to test:
    a: Set slave address
    b: Write byte to register
    c: Write 2 bytes to register
    d: Read byte from register
    e: Read 2 bytes from register
    q: Quit

Select a function (a,b,c,d,e) to test or q to quit. You will be prompted for read, write and register values as appropriate. Test results will be displayed in the terminal.

Test Options

• Set Slave Address
  Press the A key to select the Set slave address function, then press Enter.

  Select a function to test:
      a: Set slave address
      b: Write byte to register
      c: Write 2 bytes to register
      d: Read byte from register
      e: Read 2 bytes from register
      q: Quit
  >> a
  
  
  Enter the slave address (in hex): 48
  
  Calling i2c_set_slave(3, 0x48)
  i2c_set_slave reports success
  

  The slave address receives the clock and responds when addressed by the master.

  This function is to set the slave address of the I²C device. This only need to be done once to initialize the address and then each time that a new device is addressed.

• Write byte to register
  Press the B key to select the Write byte to register function, then press Enter

  Select a function to test:
      a: Set slave address
      b: Write byte to register
      c: Write 2 bytes to register
      d: Read byte from register
      e: Read 2 bytes from register
      q: Quit
  >> b
  
  Enter a byte to write (in hex): aa
  Enter a register value to write (in hex): 01
  
  Calling i2c_write_cmd(3, 0x1, 0xAA)
  i2c_write_cmd reports success
  

  This function uses the Linux write system call to write one byte to the selected register on the I²C device.

• Write 2 bytes to register
  Press the C key to select the Write 2 bytes to register function, then press Enter.

  Select a function to test:
      a: Set slave address
      b: Write byte to register
      c: Write 2 bytes to register
      d: Read byte from register
      e: Read 2 bytes from register
      q: Quit
  >> c
  
  Enter a 2 byte number to write (in hex): aabb
  Enter a register value to write (in hex): 01
  
  Calling i2c_write_cmd2(3, 0x1, 0xAABB)
  i2c_write_cmd2 reports success
  

  This function uses the same system call as the previous option, but writes 2 bytes to a register instead of just one.

• Read byte from register
  Press the D key to select the Read byte from register function, then press Enter.

  Select a function to test:
      a: Set slave address    
      b: Write byte to register    
      c: Write 2 bytes to register    
      d: Read byte from register    
      e: Read 2 bytes from register    
      q: Quit
  >> d
  
  Enter a register value to read from (in hex): bb
  
  Calling i2c_read_reg(3, (__u8 *)&val, 0xBB)
  i2c_read_reg reports success
  Read value 0xB
  

  This function uses the Linux read system call to read a byte to the selected register on the I²C device.

• Read 2 bytes from register
  Press the E key to select the Read 2 bytes from register function, then press Enter.

  Select a function to test:
      a: Set slave address        
      b: Write byte to register        
      c: Write 2 bytes to register        
      d: Read byte from register        
      e: Read 2 bytes from register        
      q: Quit
  >> e
  
  Enter a register value to read from (in hex): bbcc
  
  Calling i2c_read_reg2(3, &val, 0xBBCC)
  i2c_read_reg2 reports success
  Read value 0xB0B
  

  This function uses the same system call as the previous option, but shifts to the right.

  The i2c_test example writes a byte to a selected register. The register then reads the byte, shifts the byte 8 bits to the right and then reads the address to the selected register on the I²C device.

  • Quit
    

  Press the Q key to quit out of the i2c_test example, then press Enter.

  Select a function to test:    
      a: Set slave address            
      b: Write byte to register            
      c: Write 2 bytes to register            
      d: Read byte from register            
      e: Read 2 bytes from register            
      q: Quit
  >> q
  Quiting...
  

  This function quits you out of the i2c_test example on the I²C device.

Real-World Example

Hardware Requirements

The i2c_test C Real-World example project will be running on an EMAC SOM-210ES carrier board. This example will be communicating with the RTC clock on the SOM-3517M.

For more information about the RTC Clock see the following page for the data sheet: http://www.nxp.com/documents/data_sheet/PCA8565.pdf

Using Real-World Example i2c_test

Just like before, the i2c_test program is executed from the console. It takes no parameters.

root@emac-oe~:$ ./i2c_test

A menu will appear in the terminal:

Select a function to test:
    a: Set slave address
    b: Write byte to register
    c: Write 2 bytes to register
    d: Read byte from register
    e: Read 2 bytes from register
    q: Quit

Test Options

• Set Slave Address
  

Press the A key to select the Set slave address function, then press Enter.

The RTC Clock slave address in binary is 1010001 (58 in Hexadecimal).

The slave address must be shifted to the right

Select a function to test:
    a: Set slave address
    b: Write byte to register
    c: Write 2 bytes to register
    d: Read byte from register
    e: Read 2 bytes from register
    q: Quit
>> a

Enter the slave address (in hex): 28

Calling i2c_set_slave(3, 0x48)
i2c_set_slave reports success

Summary

The i2c_test C example project writes and reads bytes to a selected register on the I²C device.