diff --git a/driver-vpi/main.c b/driver-vpi/main.c
index 130efe464..d208764cd 100644
--- a/driver-vpi/main.c
+++ b/driver-vpi/main.c
@@ -1,38 +1,59 @@
+/*
+ * Copyright (c) 2002 Gus Baldauf (gus@picturel.com)
+ *
+ *    This source code is free software; you can redistribute it
+ *    and/or modify it in source code form under the terms of the GNU
+ *    General Public License as published by the Free Software
+ *    Foundation; either version 2 of the License, or (at your option)
+ *    any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program; if not, write to the Free Software
+ *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
 /*
  *	iverilog-vpi.c
  *
- *	this program is provides the functionality
- *	of iverilog-vpi.sh under Win32
+ *	this program provides the functionality of iverilog-vpi.sh under Win32
  */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
+#include <sys/types.h>
+#include <sys/stat.h>
+
 #include <windows.h>
 
 /* Macros used for compiling and linking */
 
-#define IVERILOG_VPI_CC        "gcc"
-#define IVERILOG_VPI_CXX       "gcc"
+#define IVERILOG_VPI_CC        "gcc"				/* no .exe extension  */
+#define IVERILOG_VPI_CXX       "gcc"				/* no .exe extension  */
 #define IVERILOG_VPI_CFLAGS    "-O"					/* -I appended  later */
-#define IVERILOG_VPI_LD        "gcc"
+#define IVERILOG_VPI_LD        "gcc"				/* no .exe extension  */
 #define IVERILOG_VPI_LDFLAGS   "-shared -Wl,--enable-auto-image-base"
 #define IVERILOG_VPI_LDLIBS    "-lveriuser -lvpi"	/* -L prepended later */
 
 /* pointers to global strings */
 
 static struct global_strings {
-	char *pCCSRC;		// list of C source files
-	char *pCXSRC;		// list of C++ source files
-	char *pOBJ;			// list of object files
-	char *pLIB;			// list of library files
-	char *pOUT;			// output file name (.vpi extension)
-	char *pMINGW;		// path to MinGW directory
-	char *pIVL;			// path to IVL directory
-	char *pCFLAGS;		// CFLAGS option
-	char *pLDLIBS;		// LDLIBS option
-	char *pNewPath;		// new PATH environment variable setting
+	char *pCCSRC;		/* list of C source files */
+	char *pCXSRC;		/* list of C++ source files */
+	char *pOBJ;			/* list of object files */
+	char *pLIB;			/* list of library files */
+	char *pOUT;			/* output file name (.vpi extension), if 0 length then no source files specified */
+	char *pMINGW;		/* path to MinGW directory */
+	char *pIVL;			/* path to IVL directory */
+	char *pCFLAGS;		/* CFLAGS option */
+	char *pLDLIBS;		/* LDLIBS option */
+	char *pNewPath;		/* new PATH environment variable setting */
 } gstr;
 
 
@@ -61,9 +82,11 @@ static void myExit(int exitVal)
 
 /* display usage summary and exit */
 
-static void usage(char *name)
+static void usage()
 {
-	fprintf(stderr,"usage: %s [--name=name] [-llibrary] [-mingw=dir] [-ivl=dir] sourcefile...\n",name);
+	fprintf(stderr,"usage: iverilog-vpi [--name=name] [-llibrary] [-mingw=dir] [-ivl=dir] sourcefile...\n");
+	fprintf(stderr,"   or  iverilog-vpi -mingw=dir\n");
+	fprintf(stderr,"   or  iverilog-vpi -ivl=dir\n");
 	myExit(1);
 }
 
@@ -204,7 +227,7 @@ static int GetRegistryKey(char *key, char **value)
 		fprintf(stderr,"error: out of memory\n");
 		myExit(4);
 	}
-	regKeyBuffer[regKeySize] = 0;		// makes sure there is a trailing NULL
+	regKeyBuffer[regKeySize] = 0;		/* makes sure there is a trailing NULL */
 
 	lrv = RegQueryValueEx(hkKey,key,NULL,&regKeyType,regKeyBuffer,&regKeySize);
 	if ((lrv != ERROR_SUCCESS) || (regKeyType != REG_SZ) || (!regKeySize)) {
@@ -241,13 +264,16 @@ static void SetRegistryKey(char *key, char *value)
 
 	RegSetValueEx(hkKey,key,0,REG_SZ,value,strlen(value)+1);
 	RegCloseKey(hkKey);
+
+	printf("info:  storing %s in Windows' registry entry\n",value);
+	printf("       HKEY_LOCAL_MACHINE\\Software\\Icarus Verilog\\%s\n",key);
 }
 
 /* parse the command line, assign results to global variable strings */
 
 static int parse(int argc, char *argv[])
 {
-	int idx;
+	int idx, srcFileCnt=0;
 
 	char dot_c_ext[]    = ".c";
 	char dot_cc_ext[]   = ".cc";
@@ -262,18 +288,21 @@ static int parse(int argc, char *argv[])
 
 	for (idx=1; idx<argc; ++idx) {
 		if (endsIn(dot_c_ext,argv[idx])) {				/* check for C source files */
+			++srcFileCnt;
 			append(&gstr.pCCSRC,argv[idx]);
 			append(&gstr.pCCSRC," ");
 			if (!*gstr.pOUT)
 			   assignn(&gstr.pOUT,argv[idx],strlen(argv[idx])-strlen(dot_c_ext));
 		}
 		else if (endsIn(dot_cc_ext,argv[idx])) {		/* check for C++ source files */
+			++srcFileCnt;
 			append(&gstr.pCXSRC,argv[idx]);
 			append(&gstr.pCXSRC," ");
 			if (!*gstr.pOUT)
 			   assignn(&gstr.pOUT,argv[idx],strlen(argv[idx])-strlen(dot_cc_ext));
 		}
 		else if (endsIn(dot_o_ext,argv[idx])) {			/* check for compiled object files */
+			++srcFileCnt;
 			append(&gstr.pOBJ,argv[idx]);
 			append(&gstr.pOBJ," ");
 			if (!*gstr.pOUT)
@@ -294,61 +323,123 @@ static int parse(int argc, char *argv[])
 			return 0;	/* different from iverilog-vpi.sh, we don't ignore accept arguments */
 	}
 
-	if (!*gstr.pOUT)
-		usage(argv[0]);
+	if (0 == srcFileCnt)
+		assign(&gstr.pOUT,"");				/* in case they used --name with no source files */
 
-	append(&gstr.pOUT,".vpi");		/* the result file should have a .vpi extension */
-	append(&gstr.pOUT," ");
+	if (!*gstr.pOUT) {						/* normally it's an error if there are no *.c,*.cc,*.o files */
+		if (!*gstr.pMINGW && !*gstr.pIVL)	/* unless they are just setting the IVL or MinGW registry entries */
+			usage();
+	}
+	else {
+		append(&gstr.pOUT,".vpi");			/* the result file should have a .vpi extension */
+		append(&gstr.pOUT," ");
+	}
 
 	return 1;
 }
 
-/* see if we can find iverilog and mingw */
+/* do minimal check that the MinGW root directory looks valid */
+
+static void checkMingwDir(char *root)
+{
+	int irv;
+	struct _stat stat_buf;
+
+	char *path;
+	initDynString(&path);
+	assign(&path,gstr.pMINGW);
+	appendBackSlash(&path);
+	append(&path,"bin\\" IVERILOG_VPI_CC ".exe");
+
+	irv = _stat(path,&stat_buf);
+	deInitDynString(path);
+
+	if (irv) {
+		fprintf(stderr,"error: %s does not appear to be the valid root directory\n",root);
+		fprintf(stderr,"       of MinGW.  Use the -mingw option of iverilog-vpi.exe to\n");
+		fprintf(stderr,"       point to the MinGW root directory.  For a Windows command\n");
+		fprintf(stderr,"       shell the option would be something like -mingw=c:\\mingw\n");
+		fprintf(stderr,"       For a Cygwin shell the option would be something like\n");
+		fprintf(stderr,"       -mingw=c:\\\\mingw\n");
+		myExit(5);
+	}
+}
+
+/* do minimal check that the Icarus Verilog root directory looks valid */
+
+static void checkIvlDir(char *root)
+{
+	int irv;
+	struct _stat stat_buf;
+
+	char *path;
+	initDynString(&path);
+	assign(&path,gstr.pIVL);
+	appendBackSlash(&path);
+	append(&path,"bin\\vvp.exe");
+
+	irv = _stat(path,&stat_buf);
+	deInitDynString(path);
+
+	if (irv) {
+		fprintf(stderr,"error: %s does not appear to be the valid root directory of\n",root);
+		fprintf(stderr,"       Icarus Verilog.  Use the -ivl option of iverilog-vpi.exe to\n");
+		fprintf(stderr,"       point to the Icarus Verilog root directory.  For a Windows\n");
+		fprintf(stderr,"       command shell the option would be something like -ivl=c:\\iverilog\n");
+		fprintf(stderr,"       For a Cygwin shell the option would be something like\n");
+		fprintf(stderr,"       -ivl=c:\\\\iverilog\n");
+		myExit(6);
+	}
+}
+
+/* see if we can find mingw root */
 
 #define IVL_REGKEY_MINGW "MingwDir"
 
 static void setup_mingw_environment()
 {
-	char *pOldPATH;
+	char *pOldPATH = getenv("PATH");		/* get current path */
 	
-	char *RegKeyMinGW;
-	initDynString(&RegKeyMinGW);
-
-	if (*gstr.pMINGW)
+	if (*gstr.pMINGW) {
+		checkMingwDir(gstr.pMINGW);
 		SetRegistryKey(IVL_REGKEY_MINGW,gstr.pMINGW);
+	}
 	else
-		if (!GetRegistryKey(IVL_REGKEY_MINGW,&RegKeyMinGW)) {
-			fprintf(stderr,"error: can not locate MinGW directory, use the -mingw option\n");
-			deInitDynString(RegKeyMinGW);
+		if (!GetRegistryKey(IVL_REGKEY_MINGW,&gstr.pMINGW)) {
+			fprintf(stderr,"error: can not locate the MinGW root directory, use the -mingw option of\n");
+			fprintf(stderr,"       iverilog-vpi.exe to point to the MinGW root directory.  For\n");
+			fprintf(stderr,"       a Windows command shell the option would be something like\n");
+			fprintf(stderr,"       -mingw=c:\\mingw  For a Cygwin shell the option would be\n");
+			fprintf(stderr,"       something like -mingw=c:\\\\mingw\n");
 			myExit(5);
 		}
 
-	pOldPATH = getenv("PATH");					/* get current path */
-
 	assign(&gstr.pNewPath,"PATH=");			/* create new path */
-	append(&gstr.pNewPath,*gstr.pMINGW ? gstr.pMINGW : RegKeyMinGW);
+	append(&gstr.pNewPath,gstr.pMINGW);
 	appendBackSlash(&gstr.pNewPath);
 	append(&gstr.pNewPath,"bin;");
 	append(&gstr.pNewPath,pOldPATH);
 
 	_putenv(gstr.pNewPath);					/* place new path in environment variable */
-
-	deInitDynString(RegKeyMinGW);
 }
 
+/* see if we can find iverilog root */
+
 #define IVL_REGKEY_IVL   "InstallDir"
 
 static void setup_ivl_environment()
 {
-	char *RegKeyIVL;
-	initDynString(&RegKeyIVL);
-
-	if (*gstr.pIVL)
+	if (*gstr.pIVL) {
+		checkIvlDir(gstr.pIVL);
 		SetRegistryKey(IVL_REGKEY_IVL,gstr.pIVL);
+	}
 	else
-		if (!GetRegistryKey(IVL_REGKEY_IVL,&RegKeyIVL)) {
-			fprintf(stderr,"error: can not locate Icarus Verilog directory, use the -ivl option\n");
-			deInitDynString(RegKeyIVL);
+		if (!GetRegistryKey(IVL_REGKEY_IVL,&gstr.pIVL)) {
+			fprintf(stderr,"error: can not locate the Icarus Verilog root directory, use the -ivl option\n");
+			fprintf(stderr,"       of iverilog-vpi.exe to point to the Icarus Verilog root directory.\n");
+			fprintf(stderr,"       For a Windows command shell the option would be something like\n");
+			fprintf(stderr,"       -ivl=c:\\iverilog  For a Cygwin shell the option would be something\n");
+			fprintf(stderr,"       like -ivl=c:\\\\iverilog\n");
 			myExit(6);
 		}
 
@@ -356,19 +447,17 @@ static void setup_ivl_environment()
 
 	assign(&gstr.pCFLAGS,IVERILOG_VPI_CFLAGS);
 	append(&gstr.pCFLAGS," -I");
-	append(&gstr.pCFLAGS,*gstr.pIVL ? gstr.pIVL : RegKeyIVL);
+	append(&gstr.pCFLAGS,gstr.pIVL);
 	appendBackSlash(&gstr.pCFLAGS);
 	append(&gstr.pCFLAGS,"include");
 
 	/* build up the LDFLAGS option string */
 
 	assign(&gstr.pLDLIBS,"-L");
-	append(&gstr.pLDLIBS,*gstr.pIVL ? gstr.pIVL : RegKeyIVL);
+	append(&gstr.pLDLIBS,gstr.pIVL);
 	appendBackSlash(&gstr.pLDLIBS);
 	append(&gstr.pLDLIBS,"lib ");
 	append(&gstr.pLDLIBS,IVERILOG_VPI_LDLIBS);
-
-	deInitDynString(RegKeyIVL);
 }
 
 /* compile source modules */
@@ -418,6 +507,14 @@ static void compile_and_link()
 	char *buf=0;
 	int iRet, compile_errors = 0;
 
+	/* print out the mingw and ivl directories to help the user debug problems */
+
+	printf("info:  %s will be used as the MinGW root directory.\n",gstr.pMINGW);
+	checkMingwDir(gstr.pMINGW);
+
+	printf("info:  %s will be used as the Icarus Verilog root directory.\n",gstr.pIVL);
+	checkIvlDir(gstr.pIVL);
+
 	/* compile */
 
 	compile(gstr.pCCSRC,&gstr.pOBJ,".c" ,&compile_errors,IVERILOG_VPI_CC );		/* compile the C   source files */
@@ -456,12 +553,13 @@ int main(int argc, char *argv[])
 	init();
 
 	if (!parse(argc,argv))
-		usage(argv[0]);
+		usage();
 
 	setup_mingw_environment();
 	setup_ivl_environment();
 
-	compile_and_link();
+	if (*gstr.pOUT)				/* are there any *.c,*.cc,*.o files specified */
+		compile_and_link();
 
 	myExit(0);
 }