The Ekdahl FAR - Command language: Difference between revisions

Since version 1.1 of the Ekdahl FAR Firmware, all commands are grouped in a hierarchical fashion according to their ''modules'' and each ladder in the hierarchy is separated by a period ("."), this works very much like folders or directories in a regular computer. Every ''module'' can contain both ''commands'' and other ''modules''.  

 

For instance, everything associated with the ''bowing wheel'' is now collected under "bowingwheel" ''module''. That in turn contains a "dcmotor" ''module'' which does direct control of the bowing motor, and it has a "pid" ''module'' that handles bow frequency.

bw.dcm.ru:1, bw.pid.tf:82.5</pre>Both ''bowmotorrun'' / ''bowingwheel.dcmotor.run'' and ''bowcontrolfrequency / bowingwheel.pid.targetfrequency'' takes one ''parameter'' each, ''bowmotorrun / bowingwheel.dcmotor.run'' is ''conditional'' and unless the first ''parameter'' is equal to '1' the motor will not start. The first ''parameter'' of ''bowcontrolfrequency / bowingwheel.pid.targetfrequency'' sets the frequency of the ''bowing wheel'', the instrument may not execute a ''command'' if it decides that the given ''parameters'' are outside of the working range or they are missing.

The addition of the hierarchy in the FAR 1.1 firmware isn't just to be able to group commands, but it's also to make the FAR not limited to a single set of ''modules'' (and is the first stepping stone to a ''modular'' Ekdahl FAR). In fact, you could have 12 different bowing wheel ''modules'' for 12 different strings, these would then be addressed as ''bowingwheel[0].command, bowingwheel[1].command'' etc. Anyone familiar with C programming notices that this is the standard way of ''indexing'' an array; using brackets ("[ ]"). When addressing a module without ''indexing'' as above, the FAR will do one or two things; either use the first object ("[0]") or, if the object is ''selectable'' it will use the previously selected object. To make things smoother a command can be executed on several objects at once by using ranges ("[0-4]") and comma separation ("[0, 3, 5-6]").

''Global variables'' are variables that are always available and will exist in any context. The ''global variables'' that are incorporated in the ''firmware'' as of this writing (2025-01-21) are:

These variables will contain whatever data is relevant to the <u>last midi message sent</u> and will not stay relevant beyond the reception of the last message.

Note that the first ''parameter'' for ''bowcontrolfrequency / bowingwheel.pid.targetfrequency'' is put in between double quotes ("). This is because the ''pow''-function requires the use of a comma (",") in order to separate in between its two required inputs; ''x'' and ''y''. In order for the Ekdahl FAR to know that this comma does not signal the beginning of a new ''command,'' we use quotes. Single (') and double (") quotes can be used and nested in all ''parameters'' and are <u>required</u> in a lot of circumstances, improper nesting or not using quotes can lead to the instrument not understanding the ''command string'' correctly.

By using the special command ''requestinfo / rqi'' one can request the information stored by a certain ''command'' or a state of the Ekdahl FAR. The ''rqi''-command is executed in the convention ''rqi:commandname[:optional parameters]''.  

To go back to our example of setting the bowing frequency using the ''bowcontrolfrequency''-command we can ask the Ekdahl FAR what the bowing frequency is set to by writing<pre>

</pre>Where '[irq]' denotes that the message returned is in the ''info request-''category, that it pertains to the command ''bcf'' / ''bw.pid.tf'' and has the value ''82.5''. Note that the returned ''command'' sent by an ''rqi''-command always uses the ''short name'' in order to preserve bandwidth. In the FAR 1.1 the return statement always returns the ''index'' of the ''module''(s) in question.

Most commands do not require any ''parameters'' when using the ''rqi''-command. The ''adcread'' / ''datareturn''-command is an example of a ''command'' that <u>does</u> require a ''parameter'' when used with ''rqi''. The ''adcread / datareturn-''command returns the last value read by the ''analog-to-digital converter'' in the ''Control box'', because there are 8 different channels the first ''parameter'' sets which channel to return the data for, hence executing the ''command''<pre>

To change how a certain ''MIDI message'' interacts with the Ekdahl FAR we need to change the ''commands'' or ''parameters'' sent when the message is received.  

'''FAR < 1.1:'''

The ''command'' responsible for mapping ''command strings'' to different ''MIDI messages'' is ''midieventhandler'' or ''mev'' for short. The first ''parameter'' of ''mev'' is the type of ''MIDI message'' that we want to remap

* '''''noteon''''' - Note on

* '''''noteoff''' -'' Note off

* '''''pat''' -'' Poly after touch

* '''''cat''''' - Channel after touch

* '''''pb''''' - Pitch bend

* '''''pc''''' - Program change

* '''''cc''''' - Continuous controller

The second ''parameter'' is the ''command string'' that is to be associated with the ''MIDI Message'' - with the exception of the ''cc''-type, here the second ''parameter'' is the ''controller number'' (0 - 127) and the <u>third</u> ''parameter'' is the ''command string''.

<pre>

'''FAR 1.1:'''

The ''commands'' responsible for mapping ''command strings'' to different ''MIDI messages'' are as follows

* '''noteon/non''''':commands'' - Sets the commands executed for a ''note on'' ''MIDI message''

* '''noteoff''/nof'''''<nowiki/>'':commands'' - Sets the commands executed for a ''note off MIDI message''

* '''polyaftertouch/pat''''':commands'' - Sets the commands executed for a ''poly aftertouch MIDI message''

* '''channelaftertouch/cat''''':commands'' - Sets the commands executed for a ''channel aftertouch MIDI message''

* '''pitchbend/pb''''':commands'' - Sets the commands executed for a ''pitch bend MIDI message''

* '''programchange/pc''''':commands'' - Sets the commands executed for a ''program change MIDI message''

* '''continuouscontrollerdata/ccd''''':controller:commands'' - Sets the commands executed for ''continuous controller'' no ''controller''

We can of course use the ''rqi''-command to check the current mapping, below we are asking what the current ''command string'' associated with the ''pitch bend'' ''MIDI message'' is<pre>

rqi:mev:pb

</pre>The return message tells us that the ''pitch bend MIDI message'' is executing a ''bchsh''-command with the parameter ''pitch*4''. Looking in the ''command reference'' we can see that ''bchsh'' is the ''short name'' of the ''bowcontrolharmonicshift''-command which shifts the frequency of the ''bowing wheel'' from the current frequency, the first (and only) parameter sets how much we want to shift it (depends on the ''bowcontrolharmonicshiftrange command'').

If we look in the list of ''[[The Ekdahl FAR - Command langue#Variables|variables]]'' above we can see that the ''pitch bend MIDI message'' will set the ''pitch variable'' which is indeed used. Now what is the '''*4''<nowiki/>' all about? Well the ''bchsh''-command expects a ''16-bit signed'' value, meaning that a full ''harmonic shift'' downwards is equal to -32767, a full ''harmonic shift'' upwards is 32767 and no ''harmonic shift'' is 0. The ''pitch bend MIDI message'' however is only 14-bits, meaning its range is -8192 to 8192, so in order to be able to use the entire range we have to multiply ''pitch'' by 4.

This whole thing about number of bits can seem confusing but in the end it's all about how fine control you have over things; the more possible values, the more detailed control. In fact, most ''MIDI'' values are only 7-bit (!) meaning a range of 0 - 127. While this may sound like a lot of detail for something like a volume control, it is not even close to enough resolution to for instance set the ''bowing speed''. Imagine that our lowest possible note frequency is 50 Hz, that means that with a 0-127 range we can only go from 50 Hz to 127 + 50 = 177 Hz - and with no decimals! This meager range and the very coarse steps of only 1 Hz would mean the instrument would never be able to sound in tune and wouldn't even have two octaves of range. The idea of limiting the Ekdahl FAR to what is possible through ''MIDI'' seemed like a poor choice thus it was decided that <u>most</u> parameters will instead be 16-bit.

Now let's break down what happens when this ''MIDI message'' is received, i.e. when a ''MIDI'' key is pressed down:

# ''m:0'' - Sets ''module'' to 0

# ''b:0'' - Sets ''bow'' to 0

# ''bchb:note'' - Invokes the ''bowcontrolharmonicbase-''command with the first ''parameter'' set to the ''variable note''.  

# ''bmr:1'' - Sets the ''bowmotorrun''-command to '1', starting the ''bow motor''

# ''bpid:1'' - Sets the ''bowpid''-command to '1', making sure the ''PID'' is used

# ''bpe:1'' - Sets the ''bowpressureengage'' to '1' which moves the ''bowing jack'' to the ''engage position''

# ''se:(velocity*512)*(1-notecount)'' - Executes the ''solenoidengage''-command with the value ''(velocity*512)*(1-notecount)''

# ''bcsm:0'' - Sets the ''bowcontrolspeedmode'' to '1' which enables automatic shut down of the ''bowing motor''

The first two ''commands'' are the ''module''- and ''bow-''command. These ''commands'' are is intended for future versions of the Ekdahl FAR that may contain more than one string or more than one bow per string. For now ''0'' is the only valid ''parameter'' value that will be accepted for either ''command''.''<nowiki/>''

The ''bowcontrolharmonicbase''-command sets the speed of the ''bowing wheel'' to its corresponding ''harmonic number'' but also takes into account its ''<nowiki/>'base''' which is the ''MIDI key'' that is mapped to ''harmonic number 0''.

After this the bowing motor is started and the ''PID'' is turned, now the instrument will try and make sure that the ''bowing wheel'' is at the right speed.

The ''bowing jack'' is raised to the ''engage position'', any added ''pressure modifiers'' will also be taken into account - once the ''bowing jack'' has reached its intended position the ''bowing wheel'' should (hopefully) make contact with the string and the Ekdahl FAR will start to produce sounds.

 

After this we have the ''solenoidengage''-command ''command'' that engages the ''hammer'' and uses the first and only ''parameter'' as the force used. Like with most ''commands'' the ''se''-command is 16-bit (0 - 65535) but the ''MIDI velocity variable'' is 7-bit (0 - 127), so to get the ''velocity'' variable to cover the entire range it needs to be multiplied with 512.  

 

The ''<nowiki/>'*(1-notecount)'''-part is a way of making sure that we are using ''legato'' mode, i.e. that the ''hammer'' is not triggered if a key is already held down when a new key is pressed. The ''notecount''-variable contains the number of ''MIDI'' notes currently held down.

 

Let's postulate that the Ekdahl FAR is tuned to a 'C' at 65.4Hz and has its ''base'' set to middle 'C' (''MIDI key'' no 36). We are using the equal-temperament 12-tone scale and the Ekdahl FAR is set to respond to <u>all</u> ''MIDI channels'' (omni). Without having previously held any keys we press the middle 'C' (''note'' value 36) as hard as possible (''velocity'' value ''127'') on ''MIDI channel'' number 1 (''channel'' value of 0). The Ekdahl FAR will get a ''note on MIDI message'' sent to it and from our mapping it will create the following ''command string''<pre>[irq]mev:noteon:'m:0,b:0,bchb:36,bmr:1,bpid:1,bpe:1,se:(127*512)*(1-0),bcsm:0'</pre>What has happened here is that all ''variables'' have been replaced with the values sent by the ''MIDI message''. Since those ''commands'' that doesn't have any ''variables'' with them will execute just as previously, only those ''commands'' whos ''parameters'' have changed will be explained:

# ''bchb: 36'' - The ''bowcontrolharmonicbase'' gets a value of ''36'' (middle 'C'), because ''harmonic number 0'' is mapped to this key it will set the ''bowing wheel'' frequency to the ''fundamental''; ''65.4'' Hertz

# ''se: (127*512)*(1-0)'' - the value of ''127'' comes from the ''velocity''-variable, ''127 * 512 = 65024'' which is awfully close to a maximum hammer force of 65535. Since no previous notes were held down ''notecount''  is equal to ''0'' and thus ''65024 * 1 = 65024''. The hammer is engaged with near maximum force.

[irq]mev:noteon:'m:0,b:0,bchb:48,bmr:1,bpid:1,bpe:1,se:(63*512)*(1-1),bcsm:0'

# ''bchb: 48'' - Due to the ''base'' being set to ''36'' the ''harmonic number'' is set to ''48 - 36 = 12''. Because we are using a 12-tone scale ''harmonic number 12'' is exactly one octave above the ''fundamental'' thus the speed of the ''bowing wheel'' is set to ''65.4 * 2 = 130.8'' Hertz.

# ''se: (63*512)*(1-1)'' - So ''63 * 512 = 32256'' and ''1 - 1 = 0'' thus ''32256 * 0 = 0''. When the ''solenoidengage''-command gets a ''parameter'' of ''0'' it will not engage the ''hammer'' - so the ''hammer'' doesn't strike

''CV Mapping'' works exactly like the ''MIDI mapping'' with the difference that the command for setting the ''CV mapping'' is different and that <u>all</u> events pertaining to this <u>only</u> change the ''value''-variable. The ''command'' for changing the ''CV mapping'' is ''adccommandmap'' or ''acm'', it take two ''parameters''; ''channel'' and ''command string''. We retrieve the ''command string'' for channel ''0'' which reads the sum of the ''harm. v/oct''-jack and the ''harmonic''-knob by sending a command of<pre>

rqi:acm:0

<pre>[irq]acm:0:'bcha:value/1327.716667-20'</pre>

 

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