All CPU intensive calculations are handled in a low prio work thread (not ecmc thread).
Communication to epics is made via a dedicated asynPortDriver (not the same that ecmc uses).

See below for configuration options and the different modes supported by this ecmc plugin.

Loading of FFT plugin in ecmc:

A plugin is loaded by the ecmccfg command loadPlugin: https://github.com/anderssandstrom/ecmccfg/blob/master/scripts/loadPlugin.cmd

Example:

 epicsEnvSet(ECMC_PLUGIN_FILNAME,"/epics/base-7.0.3.1/require/3.1.2/siteMods/ecmcPlugin_FFT/master/lib/linux-arm/libecmcPlugin_FFT.so")
 epicsEnvSet(ECMC_PLUGIN_CONFIG,"DBG_PRINT=1;SOURCE=ax1.actpos;")
 ${SCRIPTEXEC} ${ecmccfg_DIR}loadPlugin.cmd, "PLUGIN_ID=0,FILE=${ECMC_PLUGIN_FILNAME},CONFIG='${ECMC_PLUGIN_CONFIG}', REPORT=1
 epicsEnvUnset(ECMC_PLUGIN_FILNAME)
 epicsEnvUnset(ECMC_PLUGIN_CONFIG)

 dbLoadRecords(ecmcPluginFFT.template,"P=$(IOC):,INDEX=0, NELM=${FFT_NELM}")

This plugin supports multiple loading. For each load of the plugin a new FFT object will be created. In order to access these plugins, from plc:s or EPICS records, they can be accessed by an index. The first FFT plugin will have index 0. The next loaded FFT plugin will have index 1...

Note: If another plugin is loaded in between this will have no affect on these FFT indexes (so the FFT index is not the same as plugin index).

Configuration

The different available configuration settings:

SOURCE= source variable : Sets source variable for FFT (example: ec0.s1.AI_1). This config is mandatory.
DBG_PRINT=1/0 : Enables/disables printouts from plugin, default = disabled.
NFFT= nfft : Data points to collect, default = 4096.
APPLY_SCALE=1/0 : Apply scale, default = enabled.
DC_REMOVE=1/0 : Remove DC offset of input data (SOURCE), default = disabled.
ENABLE=1/0 : Enable data acq. and calcs (can be controlled over asyn), default = disabled.
MODE=CONT/TRIGG : Continious or triggered mode, defaults to TRIGG
RATE=rate in hz : fft data sample rate in hz (must be lower than ecmc rate and (ecmc_rate/fft_rate)=integer), default = ecmc rate.

Example configuration string:

"SOURCE=ax1.actpos;MODE=TRIGG;DBG_PRINT=1;ENABLE=1;"

SOURCE

The data source is defined by setting the SOURCE option in the plugin configuration string. This configuration is mandatory.

Example: Axis 1 actpos

"DBG_PRINT=1;SOURCE=ax1.actpos;"

Example: Ethercat slave 1 analog input ch1

"DBG_PRINT=1;SOURCE=ec0.s1.AI_1;"

DBG_PRINT

Enable/disable printouts from plugin can be made bu setting the "DBG_PRINT" option. The default setting is disabled.

Exmaple: Disable

"DBG_PRINT=0;SOURCE=ax1.actpos;"

NFFT

Defines number of samples for each measurement. Default setting is 4096.

Exmaple: 1024

"NFFT=1024;DBG_PRINT=0;SOURCE=ax1.actpos;"

APPLY_SCALE

Apply scaling in order to get correct amplitude of fft. Disabled as default (lower cpu usage).

Exmaple: Enable

"APPLY_SCALE=1;NFFT=1024;DBG_PRINT=0;SOURCE=ax1.actpos;"

DC_REMOVE

Remove DC of input signal. Default is disabled.

Exmaple: Enable

"DC_REMOVE=1;APPLY_SCALE=1;NFFT=1024;DBG_PRINT=0;SOURCE=ax1.actpos;"

ENABLE

Enable data acq. and FFT calcs. The default settings is disabled so needs to be enabled from plc or over asyn in order to start calculations.

Exmaple: Enable at startup

"ENABLE=1;DC_REMOVE=1;APPLY_SCALE=1;NFFT=1024;DBG_PRINT=0;SOURCE=ax1.actpos;"

MODE

The FFT module can operate in two different modes:

CONTINIOUS (CONT)
TRIGGERED (TRIGG)

Continious mode:

Clear data buffers
Wait for enable (from plc or asyn/epics record or configuration(see above))
Data acqusition starts
When buffers are full a worker thread will be triggered to calculate the FFT.
FTT results are sent by callback over asyn to epics records
goto 1.

Note: data will be "lost" during calculation time.

Triggered mode:

Clear data buffers
Wait for enable (from plc or asyn/epics record or configuration(see above))
Wait for trigger (from plc or asyn/epics record)
Data acqusition starts
When buffers are full a worker thread will be triggered to calculate the FFT.
FTT results are sent by callback over asyn to epics records
goto 1.

Exmaple: Mode triggered

"MODE=TRIGG;ENABLE=1;DC_REMOVE=1;APPLY_SCALE=1;NFFT=1024;DBG_PRINT=0;SOURCE=ax1.actpos;"

RATE

Sets the sample rate of the raw input data (from data source). The default value is the ecmc rate for that data source. Note: only a lower and "integer" division of sample rate can be defined.

Exmaple: Rate = 100Hz

RATE=100;MODE=TRIGG;ENABLE=1;DC_REMOVE=1;APPLY_SCALE=1;NFFT=1024;DBG_PRINT=0;SOURCE=ax1.actpos;"

bMeasurese

EPICS records

Each FFT plugin object will create a new asynportdriver-port named "PLUGIN.FFT" (index is explaine above). The reason for a dedicated asynport is to influence ecmc as little as possible. The plugin contains a template file that will make most information availbe from records:

Rawdata array (ro)
FFT amplitude array (result) (ro)
FFT x axis (frequencies) (ro)
Status (ro)
Mode (rw)
Sample rate (ro)
Enable cmd (rw)
Trigger cmd (rw)
NFFT (ro)

The available records from this template file can be listed by the cmd:

dbgrep *FFT*

Note: The FFT asynparameters will not be visible by the ecmcReport iocsh command since the FFT records belong to another port.

PLC interface

PLC Functions

"fft_clear(arg0);" double fft_clear(index) : Clear/reset fft[index].
"fft_enable(arg0, arg1);" double fft_enable(index, enable) : Set enable for fft[index].
"fft_trigg(arg0);" double fft_trigg(index) : Trigg new measurement for fft[index]. Will clear buffers.
"fft_mode(arg0, arg1);" double fft_mode(index, mode) : Set mode Cont(1)/Trigg(2) for fft[index].
"fft_stat(arg0);" double fft_stat(index) : Get status of fft (NO_STAT, IDLE, ACQ, CALC) for fft[index].

PLC Constants:

"fft_CONT" = 1: FFT Mode: Continious
"fft_TRIGG" = 2: FFT Mode :Triggered
"fft_NO_STAT" = 0: FFT Status: Invalid state
"fft_IDLE" = 1: FFT Status: Idle state (waiting for trigger)
"fft_ACQ" = 2: FFT Status: Acquiring data
"fft_CALC" = 3: FFT Status: Calculating result

Example script

An example script can be found in the iocsh directory of this repo. This example load 2 FFT plugin objects:

SOURCE="plcs.plc0.static.sineval" which is a plc variable updated as a sinus with default freq 5 Hz.
SOURCE="ecmc.thread.latency.max". This is the execution latency of ecmc (in nanoseconds).

Plugin info

Plugin info: 
  Index                = 1
  Name                 = ecmcPlugin_FFT
  Description          = FFT plugin for use with ecmc.
  Option description   = 
    DBG_PRINT=<1/0>    : Enables/disables printouts from plugin, default = disabled.
    SOURCE=<source>    : Sets source variable for FFT (example: ec0.s1.AI_1).
    NFFT=<nfft>        : Data points to collect, default = 4096.
    APPLY_SCALE=<1/0>  : Apply scale, default = disabled.
    DC_REMOVE=<1/0>    : Remove DC offset of input data (SOURCE), default = disabled.
    ENABLE=<1/0>       : Enable data acq. and calcs (can be controlled over asyn), default = disabled.
    MODE=<CONT/TRIGG>  : Continious or triggered mode, defaults to TRIGG
    RATE=<rate in hz>  : fft data sample rate in hz (must be lower than ecmc rate and (ecmc_rate/fft_rate)=integer), default = ecmc rate.
  Filename             = /epics/base-7.0.3.1/require/3.1.2/siteMods/ecmcPlugin_FFT/master/lib/linux-arm/libecmcPlugin_FFT.so
  Config string        = SOURCE=ecmc.thread.latency.max;DBG_PRINT=0;NFFT=1024;
  Version              = 1
  Interface version    = 512 (ecmc = 512)
     max plc funcs     = 64
     max plc func args = 10
     max plc consts    = 64
  Construct func       = @0xb5022044
  Enter realtime func  = @0xb5022090
  Exit realtime func   = @0xb502203c
  Realtime func        = @0xb5022034
  Destruct func        = @0xb502206c
  dlhandle             = @0x1d9de28
  Plc functions:
    funcs[00]:
      Name       = "fft_clear(arg0);"
      Desc       = double fft_clear(index) : Clear/reset fft[index].
      Arg count  = 1
      func       = @0xb5022094
    funcs[01]:
      Name       = "fft_enable(arg0, arg1);"
      Desc       = double fft_enable(index, enable) : Set enable for fft[index].
      Arg count  = 2
      func       = @0xb50220b0
    funcs[02]:
      Name       = "fft_trigg(arg0);"
      Desc       = double fft_trigg(index) : Trigg new measurement for fft[index]. Will clear buffers.
      Arg count  = 1
      func       = @0xb50220d4
    funcs[03]:
      Name       = "fft_mode(arg0, arg1);"
      Desc       = double fft_mode(index, mode) : Set mode Cont(1)/Trigg(2) for fft[index].
      Arg count  = 2
      func       = @0xb50220f0
    funcs[04]:
      Name       = "fft_stat(arg0);"
      Desc       = double fft_stat(index) : Get status of fft (NO_STAT, IDLE, ACQ, CALC) for fft[index].
      Arg count  = 1
      func       = @0xb5022114
  Plc constants:
    consts[00]:
      Name     = "fft_CONT" = 1.000
      Desc     = FFT Mode: Continious
    consts[01]:
      Name     = "fft_TRIGG" = 2.000
      Desc     = FFT Mode :Triggered
    consts[02]:
      Name     = "fft_NO_STAT" = 0.000
      Desc     = FFT Status: Invalid state
    consts[03]:
      Name     = "fft_IDLE" = 1.000
      Desc     = FFT Status: Idle state (waiting for trigger)
    consts[04]:
      Name     = "fft_ACQ" = 2.000
      Desc     = FFT Status: Acquiring data
    consts[05]:
      Name     = "fft_CALC" = 3.000
      Desc     = FFT Status: Calculating result