diff --git a/utils/blockwidth.py b/utils/blockwidth.py
new file mode 100644
index 00000000..ae6758cf
--- /dev/null
+++ b/utils/blockwidth.py
@@ -0,0 +1,106 @@
+#!/usr/bin/env python3
+'''
+Prints minor address group sizes
+If any part of an IP block is written, Vivado likes to write the entire block
+This can be useful to guess the number of frames an IP block uses
+
+This was developed with PERFRAMECRC, but could probably be rewritten to work without it
+'''
+
+import sys
+import os
+import time
+import json
+import subprocess
+from io import StringIO
+
+BITTOOL = os.getenv('XRAY_BITTOOL')
+
+
+def bit2packets(fn):
+    # capture_output wasn't added until 3.7, I have 3.5
+    #return subprocess.run([BITTOOL, "list_config_packets", fn], capture_output=True, check=True).stdout
+    p = subprocess.run(
+        [BITTOOL, "list_config_packets", fn],
+        check=True,
+        stdout=subprocess.PIPE)
+    return p.stdout.decode("ascii")
+
+
+def nominor(addr):
+    return addr & ~0x7f
+
+
+def gen_frame_writes(f):
+    '''
+    look for line triples like this
+
+    [Write Type=1 Address= 1 Length=         1 Reg="Frame Address"]
+    Data in hex:
+          1d 
+
+    '''
+    while True:
+        l = f.readline()
+        if not l:
+            break
+        l = l.strip()
+        # TODO: assert that writes are always per frame CRC
+        if l != '[Write Type=1 Address= 1 Length=         1 Reg="Frame Address"]':
+            continue
+        assert f.readline().strip() == 'Data in hex:'
+        lhex = f.readline().strip()
+        yield int(lhex, 16)
+
+
+def gen_major_writes(fnin):
+    '''
+    The same address can appear twice
+    Ex: 0x00800000
+    Moved from counter to set
+    '''
+    last_addrs = None
+    last_major = None
+
+    for this_minor in gen_frame_writes(StringIO(bit2packets(fnin))):
+        this_major = nominor(this_minor)
+
+        if this_major == last_major:
+            # should be no gaps
+            last_addrs.add(this_minor)
+
+            # addresses may skip back, but they don't seem to skip forward
+            # AssertionError: (0, 2, {0, 1})
+            # assert (this_major - this_minor) + 1 == len(last_addrs), (this_major, len(last_addrs), last_addrs)
+            assert (this_major - this_minor) + 1 <= len(last_addrs), (
+                this_major, len(last_addrs), last_addrs)
+        else:
+            if last_major is not None:
+                assert len(last_addrs) <= 0x80
+                yield last_major, len(last_addrs)
+
+            # all writes should start at base?
+            assert this_major == this_minor
+            last_major = this_major
+            last_addrs = set([this_minor])
+    yield last_major, len(last_addrs)
+
+
+def run(fnin, verbose=False):
+    for addr, nframes in gen_major_writes(fnin):
+        print('0x%08X: 0x%08X' % (addr, nframes))
+
+
+def main():
+    import argparse
+
+    parser = argparse.ArgumentParser(
+        description='Print PERFRAMECRC bitstream minor address gropuing')
+    parser.add_argument('fnin', default=None, help='input bitstream')
+    args = parser.parse_args()
+
+    run(args.fnin, verbose=False)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/utils/environment.sh b/utils/environment.sh
index 5545f727..fb69da52 100644
--- a/utils/environment.sh
+++ b/utils/environment.sh
@@ -24,5 +24,6 @@ export XRAY_SEGMATCH="${XRAY_TOOLS_DIR}/segmatch"
 export XRAY_SEGPRINT="python3 ${XRAY_UTILS_DIR}/segprint.py"
 export XRAY_BITS2FASM="python3 ${XRAY_UTILS_DIR}/bits2fasm.py"
 export XRAY_FASM2FRAMES="python3 ${XRAY_UTILS_DIR}/fasm2frames.py"
-
+export XRAY_BITTOOL="${XRAY_TOOLS_DIR}/bittool"
+export XRAY_BLOCKWIDTH="python3 ${XRAY_UTILS_DIR}/blockwidth.py"