--- a/.hgignore	Thu Sep 17 00:42:17 2020 +0000
+++ b/.hgignore	Thu Sep 17 00:43:26 2020 +0000
@@ -13,6 +13,7 @@
 ^fteeprom/fteeprom-erase$
 ^fteeprom/fteeprom-prog$
 ^fteeprom/fteeprom-read$
+^fteeprom/test/fteeprom-prog-bad$
 
 ^lcdtest/lcdphone$
 ^lcdtest/lcdtest$

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/fteeprom/test/Makefile	Thu Sep 17 00:43:26 2020 +0000
@@ -0,0 +1,11 @@
+CC=	gcc
+CFLAGS=	-O2
+PROGS=	fteeprom-prog-bad
+
+all:	${PROGS}
+
+fteeprom-prog-bad:	fteeprom-prog-bad.c
+	${CC} ${CFLAGS} -o $@ $@.c -lftdi
+
+clean:
+	rm -f ${PROGS} *.o *errs *.out

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/fteeprom/test/fteeprom-prog-bad.c	Thu Sep 17 00:43:26 2020 +0000
@@ -0,0 +1,123 @@
+/*
+ * This "bad" version of fteeprom-prog is being presented in order to show
+ * what happens on FT232R chips when a certain magic sequence is omitted.
+ */
+
+#include <sys/types.h>
+#include <ctype.h>
+#include <string.h>
+#include <strings.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <ftdi.h>
+
+unsigned eeprom_size;
+u_short eeprom[256];
+
+read_eeprom_common(inf, filename_for_errs)
+	FILE *inf;
+	char *filename_for_errs;
+{
+	char linebuf[1024], *cp;
+	int lineno, rc;
+	unsigned ptr = 0, input_off;
+
+	for (lineno = 1; fgets(linebuf, sizeof linebuf, inf); lineno++) {
+		for (cp = linebuf; isspace(*cp); cp++)
+			;
+		if (*cp == '\0' || *cp == '#')
+			continue;
+		if (ptr >= 256) {
+			fprintf(stderr,
+				"%s line %d: maximum EEPROM size exceeded\n",
+				filename_for_errs, lineno);
+			exit(1);
+		}
+		rc = sscanf(linebuf, "%x: %hx %hx %hx %hx %hx %hx %hx %hx",
+			    &input_off, eeprom + ptr, eeprom + ptr + 1,
+			    eeprom + ptr + 2, eeprom + ptr + 3,
+			    eeprom + ptr + 4, eeprom + ptr + 5,
+			    eeprom + ptr + 6, eeprom + ptr + 7);
+		if (rc != 9 || input_off != ptr * 2) {
+			fprintf(stderr, "%s line %d: invalid input\n",
+				filename_for_errs, lineno);
+			exit(1);
+		}
+		ptr += 8;
+	}
+	if (ptr != 64 && ptr != 128 && ptr != 256) {
+		fprintf(stderr, "%s: not an EEPROM image of recognized size\n",
+			filename_for_errs);
+		exit(1);
+	}
+	eeprom_size = ptr;
+}
+
+read_eeprom_from_file(filename)
+	char *filename;
+{
+	FILE *inf;
+
+	inf = fopen(filename, "r");
+	if (!inf) {
+		perror(filename);
+		exit(1);
+	}
+	read_eeprom_common(inf, filename);
+	fclose(inf);
+}
+
+read_eeprom_from_stdin()
+{
+	read_eeprom_common(stdin, "stdin");
+}
+
+main(argc, argv)
+	char **argv;
+{
+	struct ftdi_context ftdi;
+	u_short modem_status;
+	unsigned n;
+
+	if (argc < 2 || argc > 3) {
+		fprintf(stderr, "usage: %s device-selector [eeprom-image]\n",
+			argv[0]);
+		exit(1);
+	}
+	if (argv[2])
+		read_eeprom_from_file(argv[2]);
+	else
+		read_eeprom_from_stdin();
+	ftdi_init(&ftdi);
+	if (ftdi_usb_open_string(&ftdi, argv[1]) < 0) {
+		fprintf(stderr, "FTDI USB open failed: %s\n", ftdi.error_str);
+		exit(1);
+	}
+#if 0	/* FT232R magic sequence omitted! */
+	if (ftdi_usb_reset(&ftdi) < 0) {
+		fprintf(stderr, "ftdi_usb_reset() failed: %s\n",
+			ftdi.error_str);
+		exit(1);
+	}
+	if (ftdi_poll_modem_status(&ftdi, &modem_status) < 0) {
+		fprintf(stderr, "ftdi_poll_modem_status() failed: %s\n",
+			ftdi.error_str);
+		exit(1);
+	}
+	if (ftdi_set_latency_timer(&ftdi, 0x77) < 0) {
+		fprintf(stderr, "ftdi_set_latency_timer() failed: %s\n",
+			ftdi.error_str);
+		exit(1);
+	}
+#endif
+	for (n = 0; n < eeprom_size; n++) {
+		if (ftdi_write_eeprom_location(&ftdi, n, eeprom[n]) < 0) {
+			fprintf(stderr, "EEPROM write error: %s\n",
+				ftdi.error_str);
+			exit(1);
+		}
+	}
+	ftdi_usb_close(&ftdi);
+	exit(0);
+}