Software in the Loop

The software-in-the-loop (SIL) diagram runs the real C code of Stepper-C — the same sources that go into the firmware — against the motor model in Xcos. It is the place where a user without Scilab knowledge sees the library control a motor: open one file, press Start, watch currents, speed, load angle and position. It is also a test bench: S01–S04 compare it sample by sample with the Scilab prototype.

Start here

1. Install Scilab 2027 and, on Windows, Visual Studio 2022 or the free Build Tools with the workload Desktop development with C++.
2. Clone Stepper-C into the folder sfs-stepper-ctrl next to sfs-stepper-sim (or set the environment variable SSTEP_CTRL_DIR to it).
3. Open start_sil.sce in Scilab and press F5.
4. Xcos opens xcos/stepper_sil.zcos. Press Start (▶).

The default scenario moves the motor two revolutions (6400 microsteps at 1/16) with 5 rev/s and 50 rev/s² on the B-G431B-ESC1 at 24 V. The scope shows four plots: the phase currents with their references, the speed in rpm, the load angle in electrical degrees (above 90° the motor is close to losing steps) and the commanded and real rotor positions in microsteps.

start_sil.sce has two settings at the top:

Variable	Values	Effect
sil_backend	"FIXED" (default), "FLOAT"	numeric backend of the compiled library; switching needs a Scilab restart
sil_regenerate	%f (default), %t	%t builds the diagram again from xcos/sil_diagram.sci (needed after a change of the block interfaces)

The diagram

Block	Computational function (C, type 4)	Inputs → outputs	Parameters
SampleCLK	Xcos	→ event every Ts = 1/fs	Ts
STEPPER_CTRL	sstep_xcos_ctrl	ADC [i_a i_b vbus] (counts) → [compare(4) enabled], monitor [φ position velocity state faults iA* iB*]	sil_ctrl_rpar(mot, brd, ctl, mp, cmds)
STEPPER_PLANT	sstep_xcos_plant	[compare(4) enabled] → ADC sample, [iA iB ω θ vA vB |iA|max |iB|max]	sil_plant_rpar(mot, brd, loads, locked, 4)
STEPPER_MONITOR	sstep_xcos_monitor	plant + controller monitor → currents, rpm, load angle, positions, 12 values for the workspace	[mot.Ns, mp.M]
CMSCOPE	Xcos	4 plots	ranges from the context
TOWS_c	Xcos	→ workspace variable sil	buffer N_log
END_c	Xcos	stops at T_end	T_end

What the controller block does. At initialisation it builds a struct sstep_config from the parameter vector, calls sstep_init() (a configuration error stops the simulation with the library's status text) and sstep_enable(). On every clock event it applies the commands whose time has come, calls sstep_slow_loop() every ratio events, converts the ADC input to a struct sstep_sample, calls sstep_fast_loop() and outputs the compare values the library wrote through its pwm_write callback.

What the plant block does. It integrates the motor over one PWM period with the leg voltages of the previous period (the one-period computation delay of the MCU), using the averaged or the switching power stage (brd.stage), applies the load torque steps, and models the ADC: counts = round(zero + i / i_full · span), clamped to 0 … adc_full, and the bus voltage reading.

Scenario: the diagram context

The scenario is edited in Simulation → Set Context and evaluated before each run:

Variable	Meaning	Example
mot	motor parameters	mot.Td = 0.02; mot.Tc = 0.01; (detent, dry friction)
brd	board and power stage	brd.topology = "full"; brd.stage = "switching"; brd.vbus = 36;
ctl	current controller	ctl.bw_hz = 500;
mp	microsteps, speed and acceleration limits, run / hold current	mp.v_max = 25600; mp.i_run = 1.5;
cmds	commands [t kind value]: 1 MOVE to (µsteps), 2 RUN (µsteps/s), 3 STOP	[0 2 12800; 0.15 2 -12800]
loads	load torque steps [t TL] (N·m)	[0 0; 0.15 0.25]
locked	1: rotor locked (current loop test)	1
T_end	simulated time (s)	1.0
scope_i, scope_rpm, scope_pos	scope ranges	3, 400, 7000

Lines below // derived values (do not edit) compute Ts and the workspace buffer size. A command the library rejects (for example a RUN above v_max) stops the simulation with the command number, its time and the status text.

Results in the workspace

After a run the variable sil holds sil.time and sil.values with one row per PWM period:

Column	Quantity	Unit
1, 2	iA, iB (sampled)	A
3, 4	iA*, iB* (references)	A
5	speed	rpm
6	load angle	electrical °
7, 8	commanded position, rotor position	µsteps
9, 10	vA, vB (averaged voltage of the next period)	V
11, 12	largest |iA|, |iB| within the period (with the ripple when switching)	A

plot(sil.time, sil.values(:, 6));      // load angle
xtitle("Load angle", "t [s]", "deg el.");

Build and rebuild

sil_build(backend, force) copies the library sources and sil/c/sstep_xcos.c into sil/build/<backend>/, compiles them with the compiler Scilab finds (tbx_build_src; Visual Studio on Windows, gcc on Linux) with -DSSTEP_CFG_MATH_BACKEND=…, and links the shared library. The build happens once; it is repeated automatically when any source file differs from its copy in the build folder. sil/build/ is ignored by Git.

The library is searched in this order: SSTEP_CTRL_DIR, the submodule ext/sfs-stepper-ctrl, the sibling folder ../sfs-stepper-ctrl.

Agreement with the prototype

Test	Scenario	Criterion	Result
S01	current step 0 → 2 A, locked rotor	currents within 5 mA of the prototype	fix of an empty-command case applied; result of the re-run pending
S02	move 640 µsteps	currents < 5 mA, commanded angle identical, rotor < 0.05 µstep	1.05 mA, angle identical, rotor 0.0075 µstep
S03	8 rev/s, both topologies	current amplitude as the prototype (T09) ± 30 mA	1.862 A (two H-bridges), 1.557 A (shared leg), equal to the prototype
S04	run 4 rev/s with the switching stage	currents and peak current within 5 mA	new in this version; first run pending (the C plant equals the Python twin to 4·10⁻¹⁶)

The remaining difference comes from the quantisation the prototype does not have: ADC counts, Q15 arithmetic and integer compare values.

Troubleshooting

Symptom	Cause	Remedy
"No C compiler found by Scilab"	Visual Studio / Build Tools missing	install the C++ workload, restart Scilab
"Stepper-C sources not found"	library not next to the simulation	set SSTEP_CTRL_DIR
"wrong parameter vector (use sil_plant_rpar)"	diagram older than the blocks	set sil_regenerate = %t once, or delete xcos/stepper_sil.zcos
Changes in the C code have no effect	the old DLL is still loaded	restart Scilab (the build is redone automatically)
"The FIXED library is already linked … Restart Scilab to switch to FLOAT"	backend changed in a running session	restart Scilab
"Stepper-C: sstep_init failed: …"	configuration rejected by the library	the message names the status; check the context values
Link warnings when the diagram is generated	Xcos versions before the fix of the scope ports	regenerate the diagram with the current sil_diagram.sci