Manual:Flexible Logic

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Revision as of 22:10, 7 July 2016 by Russian (talk | contribs) (Case study #4: boost controller)
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Flexible Logic is the fanciest-schmanciest feature of rusEfi.

Flexible Logic allows advanced users to get unprecedented level of configurability for custom outputs and engine control. rusEfi supports up to 16 flexible outputs, each of these could be either an on/off or PWM signal. In case of a PWM signal the frequency is defined in the configuration and the duty cycle is dynamically controlled by the evaluated expression.

Fuel pump is already using this mechanism - see

Here are some commands to try:

eval "2 3 +" Prints the result of "2 + 3"

eval "rpm 100 max" Prints the result of "max(100, rpm)"

eval "100 200 1 if" Prints the result of "if(1, 200, 100)"

set_fsio_expression 1 "rpm" Turn output #1 hi if rpm != 0

set_fsio_output_pin 1 pd11 Tells output #1 to use pin PD11

See for list of available methods

More Examples

set_fsio_output_frequency 1 100 Tells FSIO channel #1 to output 100Hz PWM

Now, let's assume we want duty cycle to be 10% if rpm is below 1000, 90% if rpm is above 5000, and have it grow linearly from 10% to 90% between 1000 rpm and 5000 rpm. The human-readable expression for that would be

min(0.9, max(0.1, (rpm - 1000) / 4000 * 0.8))

in RPN that's

rpm 1000 - 5000 / 0.1 max 0.9 min

We can use

eval "rpm 1000 - 5000 / 0.1 max 0.9 min"

to validate and then

set_fsio_expression 1 "rpm 1000 - 5000 / 0.1 max 0.9 min"

Another version of the same logic would be

if (rpm < 1000, 0.1, if (rpm > 5000, 0.9, 0.1 + (rpm - 1000) / 4000 * 0.8))


FSIO parameters

FSIO expressions could be customized using 16 user-defined 'settings' which are stored within the configuration. To change a setting from dev console your command is set_fsio_setting INDEX VAlUE

To access for example setting #3 your FSIO expression is

3 fsio_setting

Please note that these indexes are starting with zero

FSIO digital inputs

These feature allows you to pull toggle switches state from your fsio expressions.

Case study #1: shift light

We want to turn on a warning light if RPM is above 4500

First we need to configure user output, let's use pin PE5 and index #3 for this example:

set_fsio_output_frequency 3 0

this would disable PWM on channel #3 and set this port to simple digital output mode

set_fsio_output_pin 3 PE5

Now we will set FSIO expression to control this output pin:

set_fsio_expression 3 "rpm 4500 >"

here 3 is the index of the output pin, and rpm 4500 > is RPN for rpm > 4500

Case study #2: A/C compressor control

Say we want to use PE0 as A/C toggle button, and we want A/C compressor logic to be 'if (rpm > 1200 AND A/C button is depressed) then output 200Hz @ 80% duty cycle on PB1 else output nothing on PB1'.

First we need to configure A/C button input pin which is currently implemented as analog input (that's a temporary hack) - see engineConfiguration->acSwitchAdc

set_fsio_output_pin 3 PB1

Configure output #3 to use pin PB1

set_fsio_output_frequency 3 200

Configure output #3 to use 200Hz PWM

And finally set the expression:

'set_fsio_expression 3 "0 80 rpm 1200 > ac_on_switch AND IF"'

Which is RPN for if(rpm > 1200 AND ac_on_switch, 80, 0)

Case study #3: digital inputs for extra devices


First we need to configure A/C digital input pin, we will use index 0:

set_fsio_input_pin 0 PE0

Case study #4: boost controller

Solenoid-controlled boost controller would need variable duty cycle. For example, let's use fsio table #3 to define the desired duty cycle:


Let's set PE11@200Hz as FSIO output #4

Fsio outputs.png

And now the tricky part, let's set FSIO expression on that output using the following command

set_fsio_expression 4 "rpm map 3 fsio_table"