2023-04-22 11:29:44 +02:00
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2023-04-28 12:03:56 +02:00
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<title>XSCHEM TUTORIAL: SYMBOL AND SCHEMATIC GENERATORS</title>
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2023-04-22 11:29:44 +02:00
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<a href="xschem_man.html" class="home">UP</a>
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<!-- slide title -->
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2023-04-28 12:03:56 +02:00
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<h1> TUTORIAL: SYMBOL AND SCHEMATIC GENERATORS (aka PCELLS)</h1>
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2023-04-23 11:06:08 +02:00
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<p>
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It is possible to insert a symbol by referencing a generator script instead of a <kbd>.sym</kbd> file.
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When inserting the symbol select the <kbd>All</kbd> checkbox to see all files , select the generator script,
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then in the File/Search textbox add two parenthesis <kbd>()</kbd> (or put required parameters in
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between, like <kbd>(buf)</kbd>)
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</p>
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<img src="symbol_generators01.png">
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<p>
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The symbolgen generator in this example takes either a <kbd>(buf)</kbd> or a <kbd>(inv)</kbd> parameter
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to generate a buffer or an inverter, respectively. If no parameters are given (empty parentheses) a buffer
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is generated.<br>
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In this example a tcl script is used, you can use any language you like. The script only needs to parse
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the parameters (if any) and output on standard output a regular xschem symbol file.
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2023-04-23 11:06:08 +02:00
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</p>
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<pre class="code">
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#!/bin/sh
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# the next line restarts using wish \
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exec tclsh "$0" "$@"
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set arg1 [lindex $argv 0]
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if { $arg1 eq {inv}} {
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puts {v {xschem version=3.1.0 file_version=1.2}
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K {type=subcircuit
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xvhdl_primitive=true
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xverilog_primitive=true
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xvhdl_format="@@y < not @@a after 90 ps;"
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xverilog_format="assign #90 @@y = ~@@a ;"
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format="@name @pinlist @symname wn=@wn lln=@lln wp=@wp lp=@lp"
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template="name=x1 wn=1u lln=2u wp=4u lp=2u"
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schematic=schematicgen(inv)}
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L 4 -40 0 -20 0 {}
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L 4 -20 -20 20 0 {}
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L 4 -20 -20 -20 20 {}
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L 4 -20 20 20 0 {}
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L 4 30 -0 40 -0 {}
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B 5 37.5 -2.5 42.5 2.5 {name=y dir=out }
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B 5 -42.5 -2.5 -37.5 2.5 {name=a dir=in }
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A 4 25 -0 5 180 360 {}
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T {@symname} -47.5 24 0 0 0.3 0.3 {}
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T {@name} 25 -22 0 0 0.2 0.2 {}
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T {y} 7.5 -6.5 0 1 0.2 0.2 {}
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T {a} -17.5 -6.5 0 0 0.2 0.2 {}
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}
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} else {
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puts {v {xschem version=3.1.0 file_version=1.2}
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K {type=subcircuit
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xvhdl_primitive=true
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xverilog_primitive=true
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xvhdl_format="@@y < @@a after 90 ps;"
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xverilog_format="assign #90 @@y = @@a ;"
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format="@name @pinlist @symname wn=@wn lln=@lln wp=@wp lp=@lp"
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template="name=x1 wn=1u lln=2u wp=4u lp=2u"
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schematic=schematicgen(buf)}
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L 4 20 0 40 0 {}
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L 4 -40 0 -20 0 {}
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L 4 -20 -20 20 0 {}
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L 4 -20 -20 -20 20 {}
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L 4 -20 20 20 0 {}
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B 5 37.5 -2.5 42.5 2.5 {name=y dir=out }
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B 5 -42.5 -2.5 -37.5 2.5 {name=a dir=in }
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T {@symname} -47.5 24 0 0 0.3 0.3 {}
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T {@name} 25 -22 0 0 0.2 0.2 {}
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T {y} 7.5 -6.5 0 1 0.2 0.2 {}
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T {a} -17.5 -6.5 0 0 0.2 0.2 {}
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}
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}
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</pre>
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<p>
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The <kbd>generators/test_symbolgen.sch</kbd> is a test schematic that places two instancs of this
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symbol generator, one as <kbd>symbolgen(buf)</kbd> and one as <kbd>symbolgen(inv)</kbd>.
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The schematic implementations of these symbols are defined by the generator using a <kbd>schematic</kbd>
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attribute. The buffer will use <kbd>schematicgen(buf)</kbd> and the inverter will
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use <kbd>schematicgen(inv)</kbd>, these schematic names are referencing a schematic generator
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script instead of regular schematic files. See next section about schematic generators.
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</p>
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<img src="symbol_generators02.png">
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<p>
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The following is the extracted netlist from this example:
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</p>
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<pre class="code">
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2023-04-23 11:06:08 +02:00
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** sch_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/test_symbolgen.sch
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**.subckt test_symbolgen
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x1 IN_INV IN symbolgen_inv wn=1u lln=2u wp=4u lp=2u
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x3 IN_BUF IN symbolgen_buf wn=1u lln=2u wp=4u lp=2u
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C1 IN_BUF 0 100f m=1
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C2 IN_INV 0 100f m=1
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**** begin user architecture code
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2023-04-27 23:51:42 +02:00
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.include models_rom8k.txt
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.param vcc=3
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vvcc vcc 0 dc 3
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Vin in 0 pwl 0 0 100n 0 100.1n 3 200n 3 200.1n 0
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.control
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save all
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tran 1n 300n uic
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write test_symbolgen.raw
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.endc
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**.ends
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* expanding symbol: symbolgen(inv) # of pins=2
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** sym_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/symbolgen
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** sch_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/schematicgen
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.subckt symbolgen_inv y a wn=1u lln=2u wp=4u lp=2u
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*.opin y
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*.ipin a
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m2 y a VCC VCC cmosp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1
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m1 y a 0 0 cmosn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1
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.ends
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* expanding symbol: symbolgen(buf) # of pins=2
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** sym_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/symbolgen
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** sch_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/schematicgen
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.subckt symbolgen_buf y a wn=1u lln=2u wp=4u lp=2u
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*.opin y
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*.ipin a
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m2 net1 a VCC VCC cmosp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1
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m1 net1 a 0 0 cmosn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1
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m3 y net1 VCC VCC cmosp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1
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m4 y net1 0 0 cmosn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1
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.ends
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.GLOBAL VCC
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.end
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</pre>
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<p>
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This approach allows to create polymorphic symbols. Multiple parameters may be given to the generator script,
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like <kbd>symbolgen(inv,hv,100)</kbd>. Xschem will call the symbolgen script with the following command:
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<kbd>symbolgen inv hv 100</kbd> and take the standard output from the script as the symbol
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file to load and display.
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</p>
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2023-04-28 12:03:56 +02:00
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<h2> Schematic generators (pcells)</h2>
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<p>
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The same approach used for symbol generators can be used for schematic generators. If you add a
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<kbd>schematic=schematicgen(buf,4)</kbd> attribute to an instance
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xschem will look for a script named <kbd>schematicgen</kbd> in the search paths and call
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it with the given parameters (that is, execute the command
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<kbd>schematicgen buf 4</kbd>) and read the produced output as a schematic file.
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</p>
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<img src="symbol_generators03.png">
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<br><br><br>
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2023-04-22 11:29:44 +02:00
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<!-- end of slide -->
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