Add additional examples of Verilog co-simulation and share the Verilog

source and large parts of the example circuits between Verilator and
Icarus Verilog.  Verilog source file adc.v has improved style:
all assignments in the always block are now non-blocking.

examples/xspice/icarus_verilog/555.cir

@@ -0,0 +1,10 @@
+Verilog-controlled simple timer.
+
+* This is the model for an RS flip-flop implemented by Icarus Verilog.
+
+.model vlog_ff d_cosim simulation="ivlng" sim_args=["555"]
+
+* The bulk of the circuit is in a shared file.
+
+.include ../verilator/555.shared
+.end

examples/xspice/icarus_verilog/README.txt

@@ -0,0 +1,46 @@
+The circuits in this directory illustrate the use of the d_cosim
+XSPICE code model as a container for a Verilog simulation using
+Icarus Verilog.  Icarus Verilog must be built with the --enable-libvvp option,
+so that its simulation engine is available as a dynamic library.
+The Verilog source code and included parts of the circuit definitions
+can be found in the adjacent "verilator" directory.
+
+The example circuits are:
+
+555.cir: The probably familiar NE555 oscillator provides a minimal example
+of combined simulation with SPICE and Verilog.
+The digital part of the IC, a simple SR flip-flop, is expressed in Verilog.
+
+delay.v: A very simple example of using delays in Verilog to generate
+waveform outputs.
+
+pwm.c: Verilog delays controlling a pulse-width modulated output generate
+an approximate sine wave.
+
+adc.cir: Slightly more complex Verilog describes the controlling part
+of a switched-capacitor ADC.
+
+Before a simulation can be run, the associated Verilog code must be compiled:
+
+    iverilog -o 555 ../verilator/555.v
+
+Similar compilations are needed to prepare the other examples.
+
+The simulations require additional dynamic libraries, ivlng.so (or ivlng.DLL)
+and ivlng.vpi: they are expected to be in the usual installation location.
+
+To use the versions in a built source tree that has not been installed,
+the .model definitions in the circuit files must be changed to the ugly:
+
+.model vlog_ff d_cosim sim_args=["555"]
++ simulation = "../../../release/src/xspice/verilog/.libs/ivlng"
++ lib_args = [ "libvvp"
++ "../../../release/src/xspice/verilog/.libs/ivlngvpi.so" ]
+
+Or for Windows builds using MSVC:
+
+.model vlog_ff d_cosim sim_args=["555"]
++ simulation = "..\..\..\visualc\xspice\verilog\ivlng.DLL"
++ lib_args = [ "libvvp"
++ "..\..\..\visualc\xspice\verilog\shim.vpi" ]
+

examples/xspice/icarus_verilog/adc.cir

@@ -0,0 +1,10 @@
+Simulation of a switched-capacitor SAR ADC with Verilator and d_cosim
+
+* Model line for the digital control implemented by Icarus Verilog.
+
+.model dut d_cosim simulation="ivlng" sim_args=["adc"]
+
+* The bulk of the circuit is in a shared file.
+
+.include ../verilator/adc.shared
+.end

examples/xspice/icarus_verilog/delay.cir

@@ -0,0 +1,10 @@
+* Waveform generation by Verilog delays
+
+adut null [ d4 d3 d2 d1 d0 ] ring
+.model ring d_cosim simulation="ivlng" sim_args = [ "delay" ]
+
+.control
+tran 20u 100u
+plot d4 d3 d2 d1 d0 digitop
+.endc
+.end

examples/xspice/icarus_verilog/pwm.cir

@@ -0,0 +1,12 @@
+* Waveform generation by PWM in Verilog
+
+adut null [ out ] pwm_sin
+.model pwm_sin d_cosim simulation="ivlng" sim_args = [ "pwm" ]
+
+r1 out smooth 100k
+c1 smooth 0 1u
+.control
+tran 1m 2
+plot out-3.3 smooth
+.endc
+.end

examples/xspice/verilator/555.cir

@@ -0,0 +1,11 @@
+Verilog-controlled simple timer.
+
+* This is the model for an RS flip-flop implemented by Verilator.
+
+.model vlog_ff d_cosim simulation="./555"
+
+* The bulk of the circuit is in a shared file.
+
+.include 555.shared
+.end
+

examples/xspice/verilator/555.shared

@@ -0,0 +1,60 @@
+* This file is not intended to be used directly, but by 555.cir.
+* That allows it to be shared by different implemnetations.
+
+* This sub-circuit simulates the NE555 timer IC, with the very simple
+* digital part as a Verilog module.
+
+.subckt NE555 trigger threshold reset control output discharge vcc ground
+
+* Resistor chain
+
+r1 vcc control 5k
+r2 control trigger_ref 5k
+r3 trigger_ref ground 5k
+
+* Two XSPICE ADC instances serve as comparators.
+
+.model comparator adc_bridge(in_low = -0.0001 in_high = 0.0001)
+athresh_comparator [%vd threshold control] [over_threshold] comparator
+atrigger_comparator [%vd trigger_ref trigger] [under_trigger] comparator
+
+* A tiny Verilog module supplies the flip-flop.
+* The model is supplied by the outer circuit file.
+
+averilog [ under_trigger over_threshold reset ] [ output qbar ] vlog_ff
+
+* The discharge transistor and its base resistor.
+
+rbase qbar discharge_base 10k
+qdischarge discharge discharge_base ground npn_transistor
+.model npn_transistor npn
+
+.ends ; Ends subcircuit NE555
+
+
+* The usual 555 oscillator with threshold connected to discharge.
+
+.param vcc=12
+
+X555 trigger_threshold trigger_threshold reset control output discharge vcc 0 ne555
+
+r1 vcc discharge 10k
+r2 discharge trigger_threshold 10k
+Ct trigger_threshold 0 1uF ic=0
+
+* A resistive load forces analog output.
+
+rload output 0 1k
+
+* A voltage source for power.
+
+Vcc vcc 0 {vcc}
+
+* Pulse the Reset signal low for 2uS each 51mS
+
+Vpulse reset 0 PULSE {vcc} 0.2 0 1u 1u 2u 51m
+
+.control
+tran 10u 200m uic
+plot trigger_threshold output x555.under_trigger-3 x555.over_threshold-1.5
+.endc

examples/xspice/verilator/555.v

@@ -0,0 +1,26 @@
+// Very simple logic for a 555 timer simulation
+
+`timescale 1us/100ns
+
+module VL555(Trigger, Threshold, Reset, Q, Qbar);
+   input wire                Trigger, Threshold, Reset; // Reset is active low.
+   output reg		     Q;
+   output wire		     Qbar;
+
+   wire			     ireset, go;
+
+   assign Qbar = !Q;
+
+   // The datasheet implies that Trigger overrides Threshold.
+
+   assign go = Trigger & Reset;
+   assign ireset = (Threshold & !Trigger) | !Reset;
+
+   initial begin
+      Q = 0;
+   end
+
+   always @(posedge(go), posedge(ireset)) begin
+      Q = go;
+   end
+endmodule

examples/xspice/verilator/README.txt

@@ -1,10 +1,32 @@
-The circuit adc.cir in this directory illustrates the use of the d_cosim
-XSPICE code model as a container for a Verilog simulation.  Before the
-simulation can be run, the Verilog code must be compiled by Verilator
-using the command:
+The circuits in this directory illustrate the use of the d_cosim
+XSPICE code model as a container for a Verilog simulation, using the
+Verilator compiler. The example circuits are:
 
-    ngspice vlnggen adc.v
+555.cir: The probably familiar NE555 oscillator provides a minimal example
+of combined simulation with SPICE and Verilog.  The digital part of the IC,
+a simple SR flip-flop, is expressed in Verilog.
 
-That should create a shared library file, adc.so (or adc.DLL on Windows)
+delay.v: A very simple example of using delays in Verilog to generate
+waveform outputs.
+
+pwm.c: Verilog delays controlling a pulse-width modulated output generate
+an approximate sine wave.
+
+adc.cir: Slightly more complex Verilog describes the controlling part
+of a switched-capacitor ADC.
+
+Before a simulation can be run, the associated Verilog code must be compiled
+by Verilator using a command script that is included with ngspice:
+
+    ngspice vlnggen 555.v
+
+That should create a shared library file, 555.so (or 555.DLL on Windows)
 that will be loaded by the d_cosim code model.  The compiled Verilog code that
-it contains will be executed during simulation.
+it contains will be executed during simulation.  Similar compilations
+are needed to prepare the other examples, but for Verilog with delays the
+command looks like:
+
+    ngspice vlnggen -- --timing delay.v
+
+(The "--" prevents "--timing" from being treated as a ngspice option, so it is
+passed on to Verilator.)

examples/xspice/verilator/adc.cir

@@ -1,103 +1,10 @@
 Simulation of a switched-capacitor SAR ADC with Verilator and d_cosim
 
-.subckt sar_adc input vref start valid d5 d4 d3 d2 d1 d0 clk
+* Model line for the digital control implemented by Verilator.
 
-* A transmission gate connects the input to the capacitor set.
+.model dut d_cosim simulation="./adc"
 
-xsample input iin sample vref tgate
-rin iin test_v 1k
+* The bulk of the circuit is in a shared file.
 
-* Capacitors and controlling inverters
-
-xb5 test_v vref d5 ccap c=1p
-xb4 test_v vref d4 ccap c={1p / 2}
-xb3 test_v vref d3 ccap c={1p / 4}
-xb2 test_v vref d2 ccap c={1p / 8}
-xb1 test_v vref d1 ccap c={1p / 16}
-xb0 test_v vref d0 ccap c={1p / 32}
-clast test_v 0            {1p / 32}
-
-* An XSPICE ADC bridge functions as a comparator.
-
-acomp [%vd(test_v vref)] [comp] comparator
-.model comparator adc_bridge in_low=0 in_high=0
-
-* The digital portion of the circuit is specified in compiled Verilog.
-* Outputs inverted to cancel the inverter in subcircuit ccap,
-* and produce the correct numerical output value.
-
-adut [ Clk Comp Start] [Sample Valid ~d5 ~d4 ~d3 ~d2 ~d1 ~d0] null dut
-.model dut d_cosim simulation="./adc.so"
-.ends // SUBCKT sar_adc
-
-* Some MOS transistors complete the circuit.
-* Models from https://homepages.rpi.edu/~sawyes/AIMSPICE_TutorialManual.pdf
-
-.model p1 pmos
-+  level=2 vto=-0.5 kp=8.5e-6 gamma=0.4 phi=0.65 lambda=0.05 xj=0.5e-6
-.model n1 nmos
-+  level=2 vto=0.5 kp=24e-6 gamma=0.15 phi=0.65 lambda=0.015 xj=0.5e-6
-
-* Use those for an inverter.
-
-.subckt ainv in out vdd
-mn out in 0 0 n1
-mp out in vdd vdd p1
-.ends
-
-* A transmission gate modelled by a switch.
-
-.subckt mos_tgate a b ctl vdd
-mn a ctl b b n1
-xinv ctl ictl vdd ainv
-mp b ictl a a p1
-.ends
-
-.subckt tgate a b ctl vdd
-switch a b ctl 0 tg
-.model tg sw vt=1.5 ron=2k
-.ends
-
-* The per-bit subcircuit in the adc
-
-.subckt ccap in vcc ctl c=10p
-xinv ctl tail vcc ainv
-cb in tail {c}
-.ends
-
-**** End of the ADC and its subcircuits.  Begin test circuit ****
-
-.param vcc=3.3
-vcc vcc 0 {vcc}
-
-* Digital clock signal
-
-aclock 0 clk clock
-.model clock d_osc cntl_array=[-1 1] freq_array=[1Meg 1Meg]
-
-* A simple DAC so that the result may be compared to the input.
-
-r5 d5 sum 2
-r4 d4 sum 4
-r3 d3 sum 8
-r2 d2 sum 16
-r1 d1 sum 32
-r0 d0 sum 64
-
-vamm sum 0 0
-
-* Pulse the Start signal high for 1.3uS each 10uS
-
-Vpulse Start 0 PULSE 0 {vcc} 0.2u 10n 10n 1.3u 10u
-Vtest input 0 PULSE 0 3 0 200u 200u 1u 401u
-
-* The ADC for testing
-
-xtest input vcc start valid d5 d4 d3 d2 d1 d0 clk sar_adc
-
-
-.control
-tran 100n 250u
-plot input xtest.test_v vamm#branch clk/2 start/3 xtest.sample/3 valid
-.endc
+.include adc.shared
 .end

examples/xspice/verilator/adc.shared

@@ -0,0 +1,107 @@
+* This file is not intended to be used directly, but by adc.cir.
+* That allows it to be shared by different implemnetations.
+
+* Simulation of a switched-capacitor SAR ADC with Verilator and d_cosim
+
+.subckt sar_adc input vref start valid d5 d4 d3 d2 d1 d0 clk
+
+* A transmission gate connects the input to the capacitor set.
+
+xsample input iin sample vref tgate
+rin iin test_v 1k
+
+* Capacitors and controlling inverters
+
+xb5 test_v vref d5 ccap c=1p
+xb4 test_v vref d4 ccap c={1p / 2}
+xb3 test_v vref d3 ccap c={1p / 4}
+xb2 test_v vref d2 ccap c={1p / 8}
+xb1 test_v vref d1 ccap c={1p / 16}
+xb0 test_v vref d0 ccap c={1p / 32}
+clast test_v 0            {1p / 32}
+
+* An XSPICE ADC bridge functions as a comparator.
+
+acomp [%vd(test_v vref)] [comp] comparator
+.model comparator adc_bridge in_low=0 in_high=0
+
+* The digital portion of the circuit is specified in compiled Verilog.
+* Outputs inverted to cancel the inverter in subcircuit ccap,
+* and produce the correct numerical output value.  The model definition
+* is supplied by the calling circuit file.
+
+adut [ Clk Comp Start] [Sample Valid ~d5 ~d4 ~d3 ~d2 ~d1 ~d0] dut
+.ends // SUBCKT sar_adc
+
+* Some MOS transistors complete the circuit.
+* Models from https://homepages.rpi.edu/~sawyes/AIMSPICE_TutorialManual.pdf
+
+.model p1 pmos
++  level=2 vto=-0.5 kp=8.5e-6 gamma=0.4 phi=0.65 lambda=0.05 xj=0.5e-6
+.model n1 nmos
++  level=2 vto=0.5 kp=24e-6 gamma=0.15 phi=0.65 lambda=0.015 xj=0.5e-6
+
+* Use those for an inverter.
+
+.subckt ainv in out vdd
+mn out in 0 0 n1
+mp out in vdd vdd p1
+.ends
+
+* A transmission gate modelled by a switch.
+
+.subckt mos_tgate a b ctl vdd
+mn a ctl b b n1
+xinv ctl ictl vdd ainv
+mp b ictl a a p1
+.ends
+
+.subckt tgate a b ctl vdd
+switch a b ctl 0 tg
+.model tg sw vt=1.5 ron=2k
+.ends
+
+* The per-bit subcircuit in the adc
+
+.subckt ccap in vcc ctl c=10p
+xinv ctl tail vcc ainv
+cb in tail {c}
+.ends
+
+**** End of the ADC and its subcircuits.  Begin test circuit ****
+
+
+.param vcc=3.3
+vcc vcc 0 {vcc}
+
+* Digital clock signal
+
+aclock 0 clk clock
+.model clock d_osc cntl_array=[-1 1] freq_array=[1Meg 1Meg]
+
+* A simple DAC so that the result may be compared to the input.
+
+r5 d5 sum 2
+r4 d4 sum 4
+r3 d3 sum 8
+r2 d2 sum 16
+r1 d1 sum 32
+r0 d0 sum 64
+
+vamm sum 0 0
+
+* Pulse the Start signal high for 1.3uS each 10uS
+
+Vpulse Start 0 PULSE 0 {vcc} 0.2u 10n 10n 1.3u 10u
+Vtest input 0 PULSE 0 3 0 200u 200u 1u 401u
+
+* The ADC for testing
+
+xtest input vcc start valid d5 d4 d3 d2 d1 d0 clk sar_adc
+
+
+.control
+tran 100n 250u
+plot input xtest.test_v vamm#branch clk/2 start/3 xtest.sample/3 valid
+.endc
+.end

examples/xspice/verilator/adc.v

@@ -1,5 +1,7 @@
 // Digital control for a successive approximation ADC with switched capacitors.
 
+`timescale 100ns/100ns
+
 module adc(Clk, Comp, Start, Sample, Done, Result);
    input wire                Clk, Comp, Start;
    output reg		     Sample, Done;
@@ -22,14 +24,12 @@ module adc(Clk, Comp, Start, Sample, Done, Result);
       if (Running) begin
 	 if (Sample) begin
 	    Sample <= 0;
-	    SR[Bits - 1] = 1;
-	    Result[Bits - 1] = 1;
+	    SR[Bits - 1] <= 1;
+	    Result[Bits - 1] <= 1;
 	 end else if (SR != 0) begin
-	    if (Comp)
-	      Result &= ~SR;
-	    SR >>= 1;
-	    Result |= SR;
-	    if (SR == 0) begin
+	    Result <= (Comp ? (Result & ~SR) : Result) | (SR >> 1);
+	    SR <= SR >> 1;
+	    if (SR == 1) begin
 	       Running <= 0;
 	       Done <= 1;
 	    end
@@ -38,8 +38,8 @@ module adc(Clk, Comp, Start, Sample, Done, Result);
 	 Running <= 1;
 	 Sample <= 1;
 	 Done <= 0;
-	 SR = 0;
-	 Result = 0;
+	 SR <= 0;
+	 Result <= 0;
       end
    end
 endmodule

examples/xspice/verilator/delay.cir

@@ -0,0 +1,11 @@
+* Waveform generation by Verilog delays
+*
+
+adut null [ d4 d3 d2 d1 d0 ] ring
+.model ring d_cosim simulation="./delay"
+
+.control
+tran 20u 100u
+plot d4 d3 d2 d1 d0 digitop
+.endc
+.end

examples/xspice/verilator/delay.v

@@ -0,0 +1,14 @@
+`timescale 1us/100ns
+
+module delay(out);
+   output reg [4:0] out;
+   reg		    t;
+
+   initial out = 0;
+   always begin
+      #1;
+      t = out[4];
+      out <<= 1;
+      out[0] = ~t;
+   end
+endmodule; // delay

examples/xspice/verilator/pwm.cir

@@ -0,0 +1,12 @@
+* Waveform generation by PWM in Verilog
+
+adut null [ out ] pwm_sin
+.model pwm_sin d_cosim simulation="./pwm"
+
+r1 out smooth 100k
+c1 smooth 0 1u
+.control
+tran 1m 2
+plot out-3.3 smooth
+.endc
+.end

examples/xspice/verilator/pwm.v

@@ -0,0 +1,34 @@
+`timescale 1us/100ns
+
+//`include "constants.vams"
+`define M_TWO_PI 6.28318530717958647652
+
+module pwm(out);
+   output reg out;
+   parameter  Cycles = 1000, Samples = 1000;
+   integer    i, j, width;
+   real	      sine;
+
+   initial begin
+      i = 0;
+      j = 0;
+      width = Cycles / 2;
+      out = 0;
+   end
+
+   always begin
+      #1;
+      ++i;
+      if (i == width)
+	out = 0;
+      if (i == Cycles) begin
+	 i = 0;
+	 ++j;
+	 if (j == Samples)
+	   j = 0;
+	 sine = $sin(j * `M_TWO_PI / Samples);
+	 width = $rtoi(Samples * (1.0 + sine) / 2.0);
+	 out = (width == 0) ? 0 : 1;
+      end
+   end
+endmodule // pwm