Derivations

A beta

The explorative DSL is a beta: it works only in a project that switches it on with [beta] dsl = true in edakit.toml, and its form may still change from one version to the next.

A derivation is a rule of edakit's that derives a part's value from the parameters, the ranges of the nets it is bound to and the entries of the parts: the series resistor of an LED from its current, a divider from its output voltage and current, a pull-up from the bus. The rule proposes, the designer chooses: it never writes a value no entry has, and the part keeps the value it is given.

edakit block add led --as STATUS --connect in=SIG --set i=4mA
edakit block add led --as STATUS --connect in=SIG --set i=2mA --part R1=C17630

--set i=4mA evaluates series_resistor with the block's own entries and the range of the net in joins (SIG, 0…3.4 V): derived 140 Ω, E24's nearest 150 Ω, the window 130…160 Ω. The block's 150 Ω fits and stays. Where the block's value lies outside, add stops and names the window and the entries of the same kind and package inside it, from the library and the project; --part R1=KEY takes one – its LCSC number, part number, value and pin map. A value no entry has is never written: the part-search skill finds one.

The record goes into the graph's derivations, in a TOML graph as a [[derivations]] table: the rule, its inputs with where each number came from, the derived value, the series' nearest value and the window, the chosen value and what it predicts. edakit graph show R3 lists it. edakit graph derive evaluates every record again with the entries as they are now, and --write rewrites those of a JSON graph.

The engine DEF holds the part to its record; it compares numbers only and never evaluates a rule:

Code	Title	Severity
DEF.derive	derived values within their window	warning, inputs: warning

Rule, why, fix and sources of each: edakit explain CODE – the explorative DSL's codes are not in the catalog.

The rules, generated from their table (edakit/lang/rules.py), each choosing from an E-series of IEC 60063:

Rule	Inputs	Output and formula	Series, window
series_resistor	i (the LED current; a range gives its centre), led (the LED – the one of the definition), in (the driving port – the one besides gnd; v_on is its range's upper bound)	value: vf(i) = vf_typ_v + rs_ohm·(i − vf_at_a); R = (v_on − vf(i)) / i	E24; one step of the series around the derived value
divider	v_out (the output voltage), i (the divider's current), in (the port whose range's upper bound is v_in)	top, bottom: R_bottom = v_out / i; R_top = (v_in − v_out) / i	E24; one step each
pullup	v (the supply: a port's upper bound or a quantity), i_sink (the sink current – the I2C table's), v_ol (the low level – the I2C table's), c_bus (optional), t_rise (optional)	value: R_min = (v − v_ol) / i_sink; R_max = t_rise / (0.8473 · c_bus), else the table's r_max_ohm; the value nearest √(R_min · R_max)	E24; [R_min, R_max]
rc	f_c (the corner frequency), c (optional), r (optional)	value: R = 1 / (2π f_c C), C = 1 / (2π f_c R)	E24 for a resistor, E6 for a capacitor; one step

The source of a block

Each block of the library is written as a definition of the circuit language, edakit/blocks/<name>.circuit, and its JSON is generated from it: python -m edakit.lang.blocks lists a JSON that differs from its source, --write writes it again, and a test holds every JSON to its source. The JSON keeps the form of handbook 14.5 and gains two keys: params, the block's parameters with their defaults ({"i": {"default": "10 mA"}}), and derivations, the rules its values are derived by – led, i2c-pullups and battery-sense have them. In a project with the DSL switched on, add --set i=4mA runs them and --part R1=KEY takes another entry where the block's value lies outside what the rule derives; without it block add adds the block as it is.