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--- gnucap:user:netlist_import_and_export:geda [2025/04/09 14:02]
felixs created
+++ gnucap:user:netlist_import_and_export:geda [2025/12/04 04:26] (current)
felixs [Parameter declarations] add example
@@ Line 1: / Line 1: @@
-=== Import and export: gEDA schematics ===
+====== Import and export: gEDA schematics ======
 The gEDA file format is well known and flexible. Today it is used in Lepton, which provides an editor similar to gschem.
-A gEDA schematic stores a circuit, and a circuit will be represented as a module. It will be represented as such, using Verilog this gives us
+A gEDA schematic stores a circuit, and in the [[.|proposed format]] a circuit will be represented as a module. Using Verilog this gives us
-<code>(* S0_vflip=-1 *)
+<code>(* S0_vflip=-1, S0_scale=.0000254 *)
 module myschematic( [ports go here] );
 [parameters..]
@@ Line 13: / Line 13: @@
-The attribute ''S0_vflip'' indicates that the y axis points down. Port connections, parameters and instances will be filled in as follows.
+The attribute ''S0_vflip'' indicates that the y axis points down. The ''S0_scale'' value accounts for gEDA coordinates in 1/1000 inch units.
+Port connections, parameters and instances will be filled in as follows.
 A schematic file is essentially composed of sections for components all of which need to be imported into a Verilog based schematic.
 Letters are used to indicate the section type, the letters discussed here are C, T and N respectively.
-== A symbol file ==
+===== Symbol files =====
-a Symbol file contains attributes, and attributes are "name=value" strings stored inside Text blocks.
+A Symbol file contains the drawing that shows a device, and also attributes, and attributes are "name=value" strings
+stored inside Text blocks.
+Symbols take the role of device prototypes in a schematic. In gEDA, a device instance carries a ''basename''
+attribute indicating the file name of the symbol used, akin to a type. But this is not the type, so we use an attribute named
+''S0_geda_basename'' to store this file name.
-== Translating C lines, the basics ==
+===== Schematics =====
+==== Translating C lines, the basics ====
 A component instance starts with a line like "C 45300 48100 1 90 0 symbol-1.sym", where "symbol-1.sym" refers to a symbol file.
@@ Line 53: / Line 60: @@
 ''(* S0_geda_symbol="resistor-1.sym", S0_x_1=44100, S0_y_1=49000, S0_x_2=45000, S0_y_2=49000 *) RESISTOR #(2k) R1 (.\1 (x_cn_2),.\2 (x_cn_3));''.
-== Translating N lines ==
+==== Translating N lines ====
 'N' mostly works like 'C', but has no symbol or device name underneath. We store them as devices of type "net" and create a label if "refdes" is not supplied by the user. For example,
@@ Line 65: / Line 72: @@
 Note that in "N" lines, gEDA stores coordinates literally.
-== The value attribute ==
+===== Parameters =====
+==== Parameter declarations ====
+A parameter in a schematic may be declared using an instance of parameter-1.sym, which carries the ''symbol=schematic-parameter'' attribute. An instance of it,
+    C 46400 43900 1 0 0 parameter-1.sym
+    {
+    T 47600 44300 5 10 1 1 0 0 1
+    refdes=bias
+    T 46500 44000 5 10 1 0 0 0 1
+    default_value=17
+    T 46400 44000 5 10 1 0 0 0 1
+    verilog_type=real
+    }
+corresponds to a parameter declaration in a Verilog module, optionally with metadata, as follows.
+    (* S0_x=46400, S0_y=43900, geda_symbol="parameter-1.sym" [more geda_metadata] *) parameter bias = 17.;
+Additional gEDA attributes such as ''verilog_type'' may be used to carry unsupported data. This needs addressing in gEDA or Lepton and is beyond the scope of the translation.
+    (* S0_x=46400, S0_y=43900, geda_symbol="parameter-1.sym" [more geda_metadata] *) parameter real bias = 17.;
+Multiple declarations in a single statement
+    parameter real a=0, b=1, c=2;
+are not supported in gEDA, but may be unrolled into multiple components.
+==== The value attribute ====
+The value attribute in gEDA translates to parameter assignments. For example
+<code>C resistor-1.sym [..]
+[..] device=resistor [..] refdes=r1 [..]
+T 1 2 3 4 [..]
+value=r=1k tnom=17 tc0=3</code>
+is represented as
+<code>
+resistor #(.r(1k), .tnom(17), .tc0(3)) r1( [..] );
+</code>
+A value string that lacks parameter names is assigned by position, e.g. ''value=1 2 3'' will be turned into ''#(1,2,3)''.
+===== Connectivity =====
+Connectivity in a Verilog-AMS netlist is simple: A connection is made by connecting a node or a (slice of a) signal to a port. In a gEDA schematic, a
+connection is made by drawing or by attribute assignments.
+==== Connections by drawing ====
+Following the "basename" attribute of a component instance reveals the geometric pins positions. There is also also a pin at each end of a net object (see ''N'' line). Pins are connected when they share the position on the screen. In addition, pins that are in between the endpoints of a net spawn an additional connection to the net. But only if the net is vertical of horizontal. For example
+  N 27100 72900 22600 66700 4
+  N 22500 72900 30800 72900 4
+means
+  (* geda_color=4, S0_x1=27100, S0_y1=72900, S0_x2=22600, S0_y2=66700 *) net #() net0 (x_nn_0,x_nn_1);
+  (* geda_color=4, S0_x1=22500, S0_y1=72900, S0_x2=30800, S0_y2=72900 *) net #() net1 (x_nn_2,x_nn_3,x_nn_0);
+==== Connections by attribute ====
+=== Base case ===
+A symbol instance that represents a device may have multiple ''net'' attributes with a value like ''A:B,C,D'', see [[https://lepton-eda.github.io/lepton-manual.html/net_003d-attribute-mini_002dHOWTO.html|Lepton manual]].
+These are translated to port assignments, and mix with other port assignments. For example
+<code>some_device #() my_refdes(.B(A), .C(A), .D(A), [..] .other(n17),[..]);.</code>
+This reflects that ''A:B,C,D'' is actually a contrived short hand syntax for 3 individual assignments.
+=== net overrides ===
+Some situations require untangling identify the intent as illustrated as follows.
+For example, the data
+  net=A:B,C // in the symbol
+  net=A:X,Y // in the instance
+  net=B:C   // in the instance
+  net=C:X   // in the instance
+would be interpreted as
+  .B(A) .C(A) .X(A) .Y(A) .C(B) .X(C) // untangled assignments in order
+  .B(A) .C(B) .X(C) .Y(A)             // effective port assignment (rightmost wins)
+Note that the instance value of "net" does not replace the value assigned in the instance as usual.
+=== Already visible case ===
+Sometimes those "net" connections correspond to named visible pins inside the symbol. The Lepton manual addresses the situation as follows.
+//Creating a ‘net=’ attribute which associates a signal name with a pin which is already visible on the symbol, is probably a bad idea. This does work, but all the ramifications have not been explored yet.//
+The "bad idea" finds use in "rail" devices that //specify power, ground, and/or arbitrary nets//. For example,
+a gnd-1.sym instance has a port named "1" and a "net=GND:1" attribute. If port "1" is connected to a (positioned) node ''n42'', we represent the instance as
+<code>net #() myground0(.\1 (n42), .rail(GND));.</code>
+Using a "net" special device to represent the rail device instance is consistent with use in gEDA/Lepton, since ''gnd-1.sym'' is not meant to carry a "device" attribute that would require otherwise.
+Following our translation, the additional "GND" node connects all gnd-1.sym instances, implementing the "net" logic, as intended. The name of the second port, "rail", is made up, for now.
+==== Port declarations ====
+A schematic essentially defines a "module" and may have ports. Lepton supplies a symbol with a single pin and a ''symbol=schematic-port'' attribute. Instances of such symbols should be used to declare ports in a schematic. The ''refdes'' attribute sets the port name.
+In older schematics ad-hoc solutions and workarounds indicating port connections can be found. For example the ''device=spice-IO'' attribute has been in wide use. Some heuristics cover some of these, but they should not be relied on.
+===== Non-circuit items =====
+==== Text ====
-TODO
+Text objects store a given positive number of lines. We can store lines in a string attribute. Here, a line ends with a newline character.
+The x/y coordinates refer to the left end of the baseline of the first line of text, and this may require some guesswork. Other attributes are named as in the manual.
+Identifiers for text are arbitrary, but assigned uniquely. Text items such as
+  T 1000 100 9 10 1 0 0 0 1
+  AAAA
+  T 2000 100 9 10 1 0 0 0 2
+  BBBB
+  BBBB
+  T 3000 100 9 10 1 0 0 0 1
+  CCCC
+may become
+  (* S0_text="AAAA\n", S0_x=1000, S0_y=100, geda_color=9, geda_size=10, geda_visibility=1, geda_show_name_value=0, geda_angle=0, geda_alignment=0 *) S__text #() geda_text_1 ();
+  (* S0_text="BBBB\nBBBB\n", S0_x=2000, S0_y=314, geda_color=9, geda_size=10, geda_visibility=1, geda_show_name_value=0, geda_angle=0, geda_alignment=0 *) S__text #() geda_text_2 ();
+  (* S0_text="CCCC\n", S0_x=3000, S0_y=100, geda_color=9, geda_size=10, geda_visibility=1, geda_show_name_value=0, geda_angle=0, geda_alignment=0 *) S__text #() geda_text_3 ();.