diff --git a/.gitignore b/.gitignore
index 6b3bb45..ff668d2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-*.vpp
+*.vvp
+*.o
diff --git a/verilog_iverilog/VPI_example/hello.o b/verilog_iverilog/VPI_example/hello.o
deleted file mode 100644
index 1e57f70..0000000
Binary files a/verilog_iverilog/VPI_example/hello.o and /dev/null differ
diff --git a/verilog_iverilog/VPI_example/hello.vpi b/verilog_iverilog/VPI_example/hello.vpi
deleted file mode 100755
index c90ff49..0000000
Binary files a/verilog_iverilog/VPI_example/hello.vpi and /dev/null differ
diff --git a/verilog_iverilog/VPI_example/hello.vvp b/verilog_iverilog/VPI_example/hello.vvp
deleted file mode 100755
index 22a18b6..0000000
--- a/verilog_iverilog/VPI_example/hello.vvp
+++ /dev/null
@@ -1,24 +0,0 @@
-#! /usr/bin/vvp
-:ivl_version "11.0 (stable)";
-:ivl_delay_selection "TYPICAL";
-:vpi_time_precision + 0;
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/system.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/vhdl_sys.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/vhdl_textio.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/v2005_math.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/va_math.vpi";
-S_0x561f1548f320 .scope module, "main" "main" 2 1;
- .timescale 0 0;
-v0x561f15457770_0 .var/i "val", 31 0;
-    .scope S_0x561f1548f320;
-T_0 ;
-    %pushi/vec4 41, 0, 32;
-    %store/vec4 v0x561f15457770_0, 0, 32;
-    %vpi_call 2 6 "$hello", v0x561f15457770_0 {0 0 0};
-    %end;
-    .thread T_0;
-# The file index is used to find the file name in the following table.
-:file_names 3;
-    "N/A";
-    "<interactive>";
-    "hello.v";
diff --git a/verilog_iverilog/counter/counter.vvp b/verilog_iverilog/counter/counter.vvp
deleted file mode 100755
index f6a15b4..0000000
--- a/verilog_iverilog/counter/counter.vvp
+++ /dev/null
@@ -1,86 +0,0 @@
-#! /usr/bin/vvp
-:ivl_version "11.0 (stable)";
-:ivl_delay_selection "TYPICAL";
-:vpi_time_precision + 0;
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/system.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/vhdl_sys.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/vhdl_textio.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/v2005_math.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/va_math.vpi";
-S_0x55d800361b40 .scope module, "test" "test" 2 1;
- .timescale 0 0;
-v0x55d800374740_0 .var "clk", 0 0;
-v0x55d800374810_0 .var "reset", 0 0;
-v0x55d8003748e0_0 .net "value", 7 0, L_0x55d8003749b0;  1 drivers
-L_0x55d8003749b0 .part v0x55d800374510_0, 0, 8;
-S_0x55d800361cd0 .scope module, "c1" "counter" 2 18, 3 1 0, S_0x55d800361b40;
- .timescale 0 0;
-    .port_info 0 /OUTPUT 9 "out";
-    .port_info 1 /INPUT 1 "clk";
-    .port_info 2 /INPUT 1 "reset";
-P_0x55d800361eb0 .param/l "WIDTH" 0 3 3, +C4<00000000000000000000000000001000>;
-v0x55d8003601f0_0 .net "clk", 0 0, v0x55d800374740_0;  1 drivers
-v0x55d800374510_0 .var "out", 8 0;
-v0x55d8003745f0_0 .net "reset", 0 0, v0x55d800374810_0;  1 drivers
-E_0x55d800360e90 .event posedge, v0x55d8003745f0_0, v0x55d8003601f0_0;
-    .scope S_0x55d800361cd0;
-T_0 ;
-    %wait E_0x55d800360e90;
-    %load/vec4 v0x55d8003745f0_0;
-    %flag_set/vec4 8;
-    %jmp/0xz  T_0.0, 8;
-    %pushi/vec4 0, 0, 9;
-    %assign/vec4 v0x55d800374510_0, 0;
-    %jmp T_0.1;
-T_0.0 ;
-    %load/vec4 v0x55d800374510_0;
-    %addi 1, 0, 9;
-    %assign/vec4 v0x55d800374510_0, 0;
-T_0.1 ;
-    %jmp T_0;
-    .thread T_0;
-    .scope S_0x55d800361b40;
-T_1 ;
-    %pushi/vec4 0, 0, 1;
-    %store/vec4 v0x55d800374810_0, 0, 1;
-    %pushi/vec4 0, 0, 1;
-    %store/vec4 v0x55d800374740_0, 0, 1;
-    %end;
-    .thread T_1;
-    .scope S_0x55d800361b40;
-T_2 ;
-    %delay 17, 0;
-    %pushi/vec4 1, 0, 1;
-    %store/vec4 v0x55d800374810_0, 0, 1;
-    %delay 11, 0;
-    %pushi/vec4 0, 0, 1;
-    %store/vec4 v0x55d800374810_0, 0, 1;
-    %delay 29, 0;
-    %pushi/vec4 1, 0, 1;
-    %store/vec4 v0x55d800374810_0, 0, 1;
-    %delay 11, 0;
-    %pushi/vec4 0, 0, 1;
-    %store/vec4 v0x55d800374810_0, 0, 1;
-    %delay 100, 0;
-    %vpi_call 2 10 "$stop" {0 0 0};
-    %end;
-    .thread T_2;
-    .scope S_0x55d800361b40;
-T_3 ;
-    %delay 5, 0;
-    %load/vec4 v0x55d800374740_0;
-    %nor/r;
-    %store/vec4 v0x55d800374740_0, 0, 1;
-    %jmp T_3;
-    .thread T_3;
-    .scope S_0x55d800361b40;
-T_4 ;
-    %vpi_call 2 21 "$monitor", "At time %t, value = %h (%0d)", $time, v0x55d8003748e0_0, v0x55d8003748e0_0 {0 0 0};
-    %end;
-    .thread T_4;
-# The file index is used to find the file name in the following table.
-:file_names 4;
-    "N/A";
-    "<interactive>";
-    "counter_tb.v";
-    "counter.v";
diff --git a/verilog_iverilog/hello_world/hello.vvp b/verilog_iverilog/hello_world/hello.vvp
deleted file mode 100755
index ef87cef..0000000
--- a/verilog_iverilog/hello_world/hello.vvp
+++ /dev/null
@@ -1,22 +0,0 @@
-#! /usr/bin/vvp
-:ivl_version "11.0 (stable)";
-:ivl_delay_selection "TYPICAL";
-:vpi_time_precision + 0;
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/system.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/vhdl_sys.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/vhdl_textio.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/v2005_math.vpi";
-:vpi_module "/usr/lib/x86_64-linux-gnu/ivl/va_math.vpi";
-S_0x561cd5980760 .scope module, "hello" "hello" 2 1;
- .timescale 0 0;
-    .scope S_0x561cd5980760;
-T_0 ;
-    %vpi_call 2 4 "$display", "Hello, World" {0 0 0};
-    %vpi_call 2 5 "$finish" {0 0 0};
-    %end;
-    .thread T_0;
-# The file index is used to find the file name in the following table.
-:file_names 3;
-    "N/A";
-    "<interactive>";
-    "hello.v";