diff --git a/src/urclock.c b/src/urclock.c
index cbfd062b..3e03f193 100644
--- a/src/urclock.c
+++ b/src/urclock.c
@@ -1142,9 +1142,6 @@ static void guessblstart(const PROGRAMMER *pgm, const AVRPART *p) {
     { 2048, 0, 0x12ab8da0, 0xca46a3ca }, // ATmegaBOOT_168_diecimila.hex
     { 2048, 0, 0x3242ddd3, 0xf3e94dba }, // ATmegaBOOT_168_ng.hex
     { 2048, 0, 0x2eed30b3, 0x47d14ffa }, // ATmegaBOOT_168_pro_8MHz.hex
-    { 4096, 0, 0xc52edd05, 0xa3371f94 }, // Caterina-LilyPadUSB.hex
-    { 4096, 0, 0x663b8f7e, 0x7efdda2b }, // Caterina-Robot-Control.hex
-    { 4096, 0, 0x3c6387e7, 0x7e96eea2 }, // Caterina-Robot-Motor.hex
     { 2048, 0, 0x1cef0d75, 0x6cfbac49 }, // LilyPadBOOT_168.hex
     { 1024, 1, 0x6ca0f37b, 0x31bae545 }, // bigboot_328.hex
     {  512, 0, 0x035cbc07, 0x24ba435e }, // optiboot_atmega168.hex
@@ -1159,6 +1156,7 @@ static void guessblstart(const PROGRAMMER *pgm, const AVRPART *p) {
     {  256, 0, 0xaa62bafc, 0xaa62bafc }, // picobootArduino8v3rc1.hex
     {  256, 0, 0x56263965, 0x56263965 }, // picobootSTK500-168p.hex
     {  512, 0, 0x3242ddd3, 0x5ba5f5f6 }, // picobootSTK500-328p.hex
+    { 3072, 0, 0x3242ddd3, 0xd3347c5d }, // optiboot_lgt8f328p.hex
   };
 
   uint8_t buf[4096], b128[128];
diff --git a/tools/bootloader-hash b/tools/bootloader-hash
new file mode 100755
index 00000000..7752708a
--- /dev/null
+++ b/tools/bootloader-hash
@@ -0,0 +1,123 @@
+#!/bin/bash
+
+# published under GNU General Public License, version 3 (GPL-3.0)
+# author Stefan Rueger, 2022
+#
+# Recursivly find in the current directory intel .hex files, which are
+# presumed to be bootloaders; create their hash table entry for urclock.c
+#
+# Background. This bash script computes the hash-sum of stk500v1 bootloaders
+# to ease the guesswork of AVRDUDE's -c urclock programmer. Urclock is
+# compatible with -c arduino, but needs to know the size of the bootloader to
+# protect it *externally* from being overwritten. In contrast to urboot,
+# optiboot et al binaries do not advertise their size and properties. Hence,
+# urclock.c maintains a table with hash-sums of popular bootloaders that are
+# out there in the wild, so the user doesn't have to know, let alone specify,
+# the size of the bootloader on their devices. This utility computes the
+# table entry from a .hex files in the directory.
+#
+# Example:
+# $ git clone git@github.com:MCUdude/optiboot_flash.git
+# $ ./bootloader-hash
+
+progname=$(basename $0)
+
+hash srec_cat 2>/dev/null || { echo $progname: package srecord is needed, try apt install srecord; exit; }
+hash cc 2>/dev/null || { echo $progname: need a C compiler; exit; }
+
+tmp=$(mktemp "$progname.XXXXXX")
+trap "rm -f $tmp $tmp.[ch]" EXIT
+
+cat >$tmp.c <<END
+// published under GNU General Public License, version 3 (GPL-3.0)
+// meta-autor Stefan Rueger, 2022
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "$tmp.h"
+
+// https://en.wikipedia.org/wiki/Jenkins_hash_function
+uint32_t jenkins_hash(const uint8_t* key, size_t length) {
+  size_t i = 0;
+  uint32_t hash = 0;
+
+  while (i != length) {
+    hash += key[i++];
+    hash += hash << 10;
+    hash ^= hash >> 6;
+  }
+  hash += hash << 3;
+  hash ^= hash >> 11;
+  hash += hash << 15;
+
+  return hash;
+}
+
+
+int main(int argc, char **argv) {
+  unsigned char reverse[4096];
+
+  if(argc != 2 || !argv[1])
+    exit(1);
+
+  int len, addr, end, flashsize, bi, ri;
+  char *base = strrchr(argv[1], '/');
+  base = base? base+1: argv[1];
+
+  memset(reverse, 0, sizeof reverse);
+
+  flashsize = bootloader_finish;
+  while(flashsize & (flashsize-1))
+    flashsize++;
+
+  int N = sizeof bootloader_length_of_sections/sizeof*bootloader_length_of_sections;
+
+  ri = 0;                       // buffer index
+  bi = sizeof bootloader-1;     // index in bootloader[] array, top to bottom
+  end = flashsize;
+  for(int i=N-1; i >= 0; i--) {
+    len = bootloader_length_of_sections[i];
+    addr = bootloader_address[i];
+    if(addr == 0)
+      break;
+    if(addr + len > end) {
+      printf("inconsistent %d + %d > %d\n", addr, len, end);
+      exit(1);
+    }
+
+    int nff = end-addr-len;
+    if(ri+nff <= (int) sizeof reverse)
+      memset(reverse+ri, 0xff, nff);
+    else {
+      printf("buffer too small %d + %d > %d\n", ri, nff, (int) sizeof reverse);
+      exit(1);
+    }
+    ri += nff;
+
+    for(int n=len; n; n--) {
+      if(ri >= (int) sizeof reverse)
+        goto done;
+      reverse[ri] = bootloader[bi];
+      ri++;
+      bi--;
+    }
+    end = addr;
+  }
+  
+done:
+  ;
+  printf("    { %4d, %d, 0x%08x, 0x%08x }, // %s\n", ri, 
+    strstr(base, "bigboot") || strstr(base, "BIGBOOT"),
+    jenkins_hash(reverse, 256), jenkins_hash(reverse, ri), base);
+}
+END
+
+
+for hn in $(find . -iname \*.hex -type f); do
+  srec_cat "$hn" -intel -o "$tmp.h" -c-array bootloader -c_compressed -line_length 96
+  cc $tmp.c -o $tmp
+  ./$tmp $hn
+done