The Endat application

Authors: Thiago Esteves (thiagocalori@gmail.com).

Introduction

This is a driver to access the position encoder that is under Endat 2.1 and/or Endat 2.2 protocol using Erlang code. The user can choose to read each position individually or configure to send the position every X milliseconds to be analysed.

                     ___________________________________________________
                    | PORT + NIFS  |   endat_driver.erl   |  endat.erl  |
   _________         ________              _____           _____________
  |ENCODER0 \ ----> | C Code | <--------> | Bin | <-----> | Extract Pos | Instance 0
  |_________/  |--> |________|            |_____| <-|     |_____________|
               |                                    |
   _________   |                                    |       _____________
  |ENCODER1 \ -|                                    |---> | Extract Pos | Instance 1
  |_________/                                             |_____________|

PS: There some improvements in the C code that can be used in other codes and not only in Erlang.

Compiling and Running

To compile and run for your machine just call the following command in the CLI:

$ make

Creating Endat devices

1> rr(endat).
[endat_info]
2> endat_sup:create_endat(0).
{ok,<0.168.0>}
3> endat:get_position().
{ok,11386608}
4> endat:get_state().
#endat_info{instance = 0,endat_version = 1,id = 51201,
            serial = 1649664,bits_pos1 = 25}
5> endat:start_read_position().
{ok,0}
P: 11387364
6> endat:stop_read_position().
{ok,0}

Endat 2.1 and Endat 2.2 CRC Calculation

This code is a good example of how to compare funtion performance using PORTs anf NIFs. The crc5 calculation has functions defined using PORT (endat_driver.erl) and NIFs (endat_crc.erl). In both cases there are functions that calculates the CRC using runtime calculation and others using lookup table. The code below show the comparison in time between all of them:

1> %% Dummy function to load nif so
1> endat_crc:makeCrcNorm(100,10000).
{ok,30}
2> %% Calculation using NIF
2> timer:tc(endat_crc, makeCrcNorm, [100,10000]).
{2,{ok,30}}
3> timer:tc(endat_crc, makeCrcNormLt, [100,10000]).
{1,{ok,30}}
4> %% Calculation using PORT
4> timer:tc(endat_driver, makeCrcNorm, [100,10000]).
{73,{ok,30}}
5> timer:tc(endat_driver, makeCrcNormLt, [100,10000]).
{62,{ok,30}}
6> %% Calculation using NIF
6> timer:tc(endat_crc, makeCrcPos, [25,0,0,0,1000,1234324343]).
{1,{ok,29}}
7> timer:tc(endat_crc, makeCrcPosLt, [25,0,0,0,1000,1234324343]).
{1,{ok,29}}
8> %% Calculation using PORT
8> timer:tc(endat_driver, makeCrcPos, [25,0,0,0,1000,1234324343]).
{43,{ok,29}}
9> timer:tc(endat_driver, makeCrcPosLt, [25,0,0,0,1000,1234324343]).
{55,{ok,29}}

Erlang Code References

http://erlang.org/doc/tutorial/c_port.html

http://erlang.org/doc/reference_manual/ports.html

https://erlang.org/doc/man/erl_nif.html#enif_make_uint

Endat References

https://www.heidenhain.de/fileadmin/pdb/media/img/383942-28_EnDat_2-2_en.pdf

https://www.endat.de/de_EN/endat2/