erl_i2c

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Erlang I2C C-Node and gen_server frontend Developed for and tested on a RaspberryPi running ArchLinux and Erlang R15B02

• erl has to be started with an valid shortname (-sname)
• a secret-cookie must be set either via a '.erlang.cookie'-file or via cmd-line option to erl (-setcookie)

Start gen_server and C-Node

The C-Node, responsible for execution of required ioctls, is started with the
start of the gen_server:

• erl_i2c:start_link()

Connect to i2c-bus

• erl_i2c:open_bus(BusNum)
  opens a i2c-bus with number BusNum - this corresponds to the device /dev/i2c-BusNum
  returns {open_bus, ok, BusNum} on success and
  {open_bus, error, Reason} on error
  (as long as the corresponding devices exist, multiple i2c-buses could be opened)

• erl_i2c:close_bus(BusNum)
  closes a previously opened i2c-bus with number BusNum
  returns {close_bus, ok} on success and
  {close_bus, error, Reason} on error

Write bytes on i2c- bus

To send data to devices connected to an i2c-bus the erl_i2c:write_byte-function is exported.
It comes in different flavours / arities:

(where 'Bus_Number', 'Device_Address' and 'Device_Register' are of type erlang::integer
and 'Device_Data' is of type erlang::binary and must not exceed a length of 32 bytes)

• write_byte(Bus_Number, Device_Address, Device_Register, Device_Data)
• write_byte(Device_Address, Device_Register, Device_Data)
• write_byte(Device_Register, Device_Data)
• write_byte(Device_Data)

returns {write_byte, ok, Bytes_Written} on success and
{write_byte, error, Reason} on error

'Bus_Number', 'Device_Address' and 'Device_Register' are remembered on consecutive writes.
As long as you're sure there's no other erlang-process accessing the bus you're using you could do:
write_byte(0, 32, 1, <<0>>),
write_byte(<<1>>),
write_byte(<<2>>).
which is the same as write_byte(0,32, 1, <<0, 1, 2>>).

Read Bytes from i2c-bus

To read data from devices connected to an i2c-bus the erl_i2c:read_byte-function is exported.
It comes in different flavours/arities:

(where 'Bus_Number', 'Device_Address', 'Data_Length' and 'Read_Data_Length' are of type erlang::integer
'Data_Length' must not exceed 32
'Read_Data' is of type erlang::binary)

• read_byte(Bus_Number, Device_Address, Device_Register, Data_Length)
• read_byte(Device_Address, Device_Register, Data_Length)
• read_byte(Device_Register, Data_Length)
• read_byte(Data_Length)

returns {read_byte, ok, Read_Data_Length, Read_Data} on success and
{read_byte, error, Reason} on error

'Bus_Number', 'Device_Address' and 'Device_Register' are remembered on consecutive reads.

Other Functions - mentioned but currently not documented

• erl_i2c:bus_info/0,1
• erl_i2c:set_address/1,2
• erl_i2c:get_address/0,1
• erl_i2c:set_bus/1
• erl_i2c:get_bus/0

Author

Christian Adams [email protected]

License

GPLv2

Disclaimer

This documentation and the documented C-Node and gen_server is far from beeing complete.