extracting disk images from an SDcard - nealcrook/multicomp6809 GitHub Wiki

An SDcard image for Multicomp6809 is created (as described here) by manipulating multiple disk images and then bolting them together. Sometimes you want to do the opposite: extract one or more disk images from an SDcard image.

The first thing to note is that you only need to do this "extract" if you created something on the disk whilst running FLEX (or whichever operating system) and you want to retain it. For example, having recompiled Adventure under FLEX you might want to keep the compiled version on the "golden" version of the disk (the version that's used to generate the SDcard image).

The script to extract disk images from an SDcard image is in the repository as bin/sd_image_extract and looks like this:

#!/bin/sh
#
# given an SDcard image file for multicomp, created by
# create_sd_image, extract .dsk images for the CamelForth
# blocks, each of the four FLEX disks, each of the four
# NITROS9 disks and the FUZIX disk.
#
# All of the offsets here need to match with the values
# in create_sd_image.

SDFILE=from_multicomp09_sd.img


echo working on $SDFILE



###############################################################
###############################################################
# CamelForth Block files; 4, 256Kbyte files
###############################################################
###############################################################

# 65MByte is block offset 1048576 * 65/512 = 133120 (0x2.0800)
# blk file is 256*1024/512=512 blocks
echo
echo "Extract FORTH Block files"
dd if=$SDFILE of=forthblk0.blk_extracted ibs=512 obs=512 skip=133120 count=512
dd if=$SDFILE of=forthblk1.blk_extracted ibs=512 obs=512 skip=133632 count=512
dd if=$SDFILE of=forthblk2.blk_extracted ibs=512 obs=512 skip=134144 count=512
dd if=$SDFILE of=forthblk3.blk_extracted ibs=512 obs=512 skip=134656 count=512



###############################################################
###############################################################
# FLEX disks
###############################################################
###############################################################
echo
echo "Extract FLEX .dsk images"

# Extract Drive 0: FLEX system disk
# (Allow) 3MBytes at offset 68MByte
# 68MByte is block offset 1048576 * 68/512 = 139264 (0x2.2000)
# img File is 2949120/512=5760 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=139264 count=5760
flex_disk_manip -insd tmp.img -out flex_drive0.dsk_extracted


# Extract Drive 1
# (Allow) 3MBytes at offset 71MByte
# 71MByte is block offset 1048576 * 71/512 = 145408 (0x2.3800)
# img File is 2949120/512=5760 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=145408 count=5760
flex_disk_manip -insd tmp.img -out flex_drive1.dsk_extracted


# Extract Drive 2
# (Allow) 3MBytes at offset 74MByte
# 74MByte is block offset 1048576 * 74/512 = 151552 (0x2.5000)
# img File is 1474560/512=2880 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=151552 count=5760
flex_disk_manip -insd tmp.img -out flex_drive2.dsk_extracted


# Extract Drive 3
# (Allow) 3MBytes at offset 77MByte
# 77MByte is block offset 1048576 * 77/512 = 157696 (0x2.6800)
# img File is 1474560/512=2880 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=157696 count=2880
flex_disk_manip -insd tmp.img -out flex_drive3.dsk_extracted


###############################################################
###############################################################
# NITROS9 disks
###############################################################
###############################################################
echo
echo "Extract NITROS9 .dsk images"

# Extract NITROS9 boot disk
# (Allow) 2MBytes at offset 80MByte, but disk is only 1MByte
# 80MByte is block offset 1048576 * 80/512 = 163840 (0x2.8000)
# img File is 1024*1024/512=2880 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=163840 count=2880
nitros9_disk_manip -insd tmp.img -out nitros9_0.dsk_extracted


# Extract NITROS extras disk 1
# use the "toolshed" utilities to create a disk image like this:
# os9 format -e -t80 -ds -dd nitros9_1.dsk -n"NitrOS-9/6809 Level 1 util disk1"
#
# (Allow) 2MBytes at offset 82MByte, but disk is only 1MByte
# 82MByte is block offset 1048576 * 82/512 = 167936 (0x2.9000)
# img File is 1024*1024/512=2880 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=167936 count=2880
nitros9_disk_manip -insd tmp.img -out nitros9_1.dsk_extracted


# Extract NITROS extras disk 2
# (Allow) 2MBytes at offset 84MByte, but disk is only 1MByte
# 84MByte is block offset 1048576 * 84/512 = 172032 (0x2.A000)
# img File is 1024*1024/512=2880 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=172032 count=2880
nitros9_disk_manip -insd tmp.img -out nitros9_2.dsk_extracted


# Extract NITROS extras disk 3
# (Allow) 2MBytes at offset 86MByte, but disk is only 1MByte
# 86MByte is block offset 1048576 * 86/512 = 176128 (0x2.B000)
# img File is 1024*1024/512=2880 blocks
dd if=$SDFILE of=tmp.img ibs=512 obs=512 skip=176128 count=2880
nitros9_disk_manip -insd tmp.img -out nitros9_3.dsk_extracted


###############################################################
###############################################################
# FUZIX disk
###############################################################
###############################################################
echo
echo "Extract FUZIX disk image"

# 32Mbyte at offset 98MByte
# 98MByte is block offset 1048576 * 98/512 = 200704 (0x3.1000)
# 32Mbyte is count 32*1024*1024/512 = 65536
# .. image is actually 32MByte minus 1 block: 65535.
dd if=$SDFILE of=fuzixfs.dsk_extracted ibs=512 obs=512 skip=200704 count=65535



# tidy up
rm -f tmp.img

If you haven't modified anything on the disk image from within FLEX, the extracted and original images should be identical -- for example, you can diff multicomp09_flex.dsk and flex_drive0.dsk_extracted and see that they are identical. They are also (of course) the same size -- so you can infer that they are the same non-doubled-up format.

Then, if you rename flex_drive0.dsk_extracted to multicomp09_flex.dsk it will become the new "golden" image and, when you create_sd_image and start FLEX using the new image, instead of a "clean" drive you will see one that contains your changes.

I recommend, though, that you don't change drive0 (multicomp09_flex.dsk) but create eg, drive1 with your own collection of stuff; that will make it easier for you to upgrade to newer versions of my system disk as they become available. If you do have suggestions for changes or additions to drive0, please let me know.