display the (optional) error information in commodore 1541 disk images in .d64 format

d64errors.py

#!/usr/bin/env python
from __future__ import division, print_function
import sys
import io
import glob
from os.path import getsize

def display_errors(filename, print_filename):
    size = getsize(filename)

    if print_filename:
        print("* %s: " % filename, end="")

    if size == 0:
        print("File is empty.")

    if size % 257 != 0:
        if size % 256 != 0:
            print("Not a valid D64 image.")
        else:
            print("No errors or error information not present.")
        return

    if print_filename:
        print("\n")

    sectors = size // 257

    with io.open(filename, "rb") as infile:
        infile.seek(256 * sectors, io.SEEK_SET)
        codes = bytearray(infile.read())

    track = 1
    sectors = 21
    pos = 0

    # Print header
    print("   %s" % "".join([str(x // 10) for x in range(21)]))
    print("   %s" % "".join([str(x %  10) for x in range(21)]))

    codemap = ["?"] * 256
    codemap[1]  = "-" # 00 no error
    codemap[2]  = "M" # 20 block header not found
    codemap[3]  = "X" # 21 no sync
    codemap[4]  = "D" # 22 data block not found
    codemap[5]  = "C" # 23 checksum error in data block
    codemap[6]  = "G" # 24 invalid gcr code in either header or data block
    codemap[9]  = "H" # 27 checksum error in header
    codemap[11] = "I" # 29 disc id mismatch

    while pos < len(codes):
        if track == 18:
            sectors = 19
        elif track == 25:
            sectors = 18
        elif track == 31:
            sectors = 17

        errstr = "".join([codemap[x] for x in codes[pos:pos+sectors]])
        print("%02d %s" % (track, errstr))

        pos += sectors
        track += 1

    print()

if len(sys.argv) >= 2:
    args = sys.argv[1:]
else:
    args = ["*.d64"]

filenames = []
for i in args:
    filenames.extend(glob.glob(i))

if len(filenames) == 0:
    print("No files found.")
    exit(1)

# Print the filename if more than one argument or argument constains a wildcard
print_filename = len(args) > 1 or any([c in args[0] for c in "*?[]"])

for filename in filenames:
    display_errors(filename, print_filename)

Invocation

d64errors.py <list of .d64 files>

• Filenames of multiple images can be given as command line arguments.
• Wildcards are accepted.
• Without arguments, all .d64 files in the current directory are processed.
• If no error information is present, that could both indicate that there were no errors or that it just wasn't included when creating the disk image.

Example output

   000000000011111111112
   012345678901234567890
01 ---------------------
02 ---------------------
03 --M------------------
04 --------------------M
05 ---------------------
06 ---------------------
07 ---------------------
08 ---------------------
09 ---------------------
10 ---------------------
11 ---------------------
12 ---------------------
13 ---------------------
14 ---------------------
15 ----M----------------
16 ---------------------
17 ---------------------
18 -------------------
19 -------------------
20 -------------------
21 -------------------
22 -M-----------------
23 ---------------M---
24 ---------HH--------
25 ------------------
26 ------------------
27 ------------------
28 ------------------
29 -----------------M
30 -----------M------
31 -----------------
32 -----------------
33 -----------------
34 ------M----------
35 -----------------

Significance of status markers

		cbm
-	no error	00
M	block header not found	20
X	no sync	21
D	data block not found	22
C	checksum error in data block	23
G	invalid gcr code in either header or data block	24
H	checksum error in header	27
I	disc id mismatch	29