--- a/.hgignore	Wed Jan 17 07:59:04 2018 +0000
+++ b/.hgignore	Wed Jan 17 19:12:32 2018 +0000
@@ -2,6 +2,7 @@
 
 ^build-
 ^helpers/build-date$
+^helpers/cfg-hdr-gen$
 ^helpers/makeline$
 ^helpers/mk-flash-script$
 ^helpers/srec4ram$

--- a/helpers/Makefile	Wed Jan 17 07:59:04 2018 +0000
+++ b/helpers/Makefile	Wed Jan 17 19:12:32 2018 +0000
@@ -1,12 +1,15 @@
 CC=	gcc
 CFLAGS=	-O2
-PROGS=	build-date makeline mk-flash-script srec4ram str2ind-ver
+PROGS=	build-date cfg-hdr-gen makeline mk-flash-script srec4ram str2ind-ver
 
 all:	${PROGS}
 
 build-date:	build-date.c
 	${CC} ${CFLAGS} -o $@ $@.c
 
+cfg-hdr-gen:	cfg-hdr-gen.c
+	${CC} ${CFLAGS} -o $@ $@.c
+
 makeline:	makeline.c
 	${CC} ${CFLAGS} -o $@ $@.c
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/helpers/cfg-hdr-gen.c	Wed Jan 17 19:12:32 2018 +0000
@@ -0,0 +1,141 @@
+/*
+ * This helper program generates the set of *.cfg header files, based on a
+ * template file and environment variables for the non-constant settings.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <string.h>
+#include <strings.h>
+
+char *infname;
+FILE *inf, *outf;
+char include_guard_symbol[32];
+char linebuf[256];
+int lineno;
+
+make_include_guard_symbol(fname)
+	char *fname;
+{
+	char *sp, *dp;
+	int c;
+
+	sp = fname;
+	dp = include_guard_symbol;
+	*dp++ = '_';
+	*dp++ = '_';
+	while (c = *sp++) {
+		if (islower(c))
+			c = toupper(c);
+		else if (c == '.')
+			c = '_';
+		*dp++ = c;
+	}
+	*dp++ = '_';
+	*dp++ = '_';
+	*dp = '\0';
+}
+
+close_output()
+{
+	if (outf) {
+		fprintf(outf, "#endif /* %s */\n", include_guard_symbol);
+		fclose(outf);
+		outf = 0;
+	}
+}
+
+bracket_line()
+{
+	char *cp;
+
+	close_output();
+	cp = index(linebuf+1, ']');
+	if (!cp) {
+		fprintf(stderr, "%s line %d: unterminated bracket line\n",
+			infname, lineno);
+		exit(1);
+	}
+	*cp = '\0';
+	outf = fopen(linebuf+1, "w");
+	if (!outf) {
+		perror(linebuf+1);
+		exit(1);
+	}
+	make_include_guard_symbol(linebuf+1);
+	fprintf(outf, "#ifndef %s\n", include_guard_symbol);
+	fprintf(outf, "#define %s\n", include_guard_symbol);
+}
+
+process_line()
+{
+	char *cp, *symbol, *value;
+
+	if (linebuf[0] == '[')
+		return bracket_line();
+	for (cp = linebuf; isspace(*cp); cp++)
+		;
+	if (*cp == '\0' || *cp == '#')
+		return;
+	for (symbol = cp; *cp && !isspace(*cp); cp++)
+		;
+	if (!*cp) {
+inv:		fprintf(stderr, "%s line %d: expected two fields\n",
+			infname, lineno);
+		exit(1);
+	}
+	*cp++ = '\0';
+	while (isspace(*cp))
+		cp++;
+	if (*cp == '\0' || *cp == '#')
+		goto inv;
+	for (value = cp; *cp && !isspace(*cp); cp++)
+		;
+	if (*cp)
+		*cp++ = '\0';
+	while (isspace(*cp))
+		cp++;
+	if (*cp != '\0' && *cp != '#')
+		goto inv;
+	if (!strcmp(value, "var")) {
+		value = getenv(symbol);
+		if (!value) {
+			fprintf(stderr,
+			"%s line %d: no environment variable named %s\n",
+				infname, lineno, symbol);
+			exit(1);
+		}
+	}
+	if (!outf) {
+		fprintf(stderr, "%s line %d: no open output file\n",
+			infname, lineno);
+		exit(1);
+	}
+	fprintf(outf, "#define %s %s\n", symbol, value);
+}
+
+main(argc, argv)
+	char **argv;
+{
+	if (argc != 3) {
+		fprintf(stderr, "usage: %s template-file output-dir\n",
+			argv[0]);
+		exit(1);
+	}
+	infname = argv[1];
+	inf = fopen(infname, "r");
+	if (!inf) {
+		perror(infname);
+		exit(1);
+	}
+	if (chdir(argv[2]) < 0) {
+		perror(argv[2]);
+		exit(1);
+	}
+	for (lineno = 1; fgets(linebuf, sizeof linebuf, inf); lineno++)
+		process_line();
+	close_output();
+	exit(0);
+}