MFM Emulator on the Commodore 900
These are my notes on using David Gesswein’s MFM emulator with the Commodore 900. At present, I do not have it set up to use the emulator on a regular basis but I was able to use it to write out a good hard drive after I had cloned and fixed the original drive.
To read a hard drive and create an extract, emulation and transitions file in one shot:
Login as “root”
./mfm_read --analyze --retries 200,8 --extracted_data_file c900.extract --emulation_file c900.emu --transitions_file c900.tran
NOTE: The analysis will give you information on your hard drive configuration. Please make a note of these in case you need to specify some of these parameters for other commands. I needed it for creating an emulator file from an extract. It will look like this in the output of the mfm_read:
... Command line to read disk: --format Intel_iSBC_214_512B --sectors 17,0 --heads 4 --cylinders 612 --header_crc 0xffff,0x1021,16,0 --data_crc 0xffffffff,0x140a0445,32,8 --sector_length 512 --retries 50,4 --drive 1 ...
To emulate with a Emulation file:
Login as “root”
./mfm_emu --drive 1 --file ../c900fixed.emu --quiet 0
To fix your image on the emulated computer (if you are able to via emulation)
- Use the emulated file to emulate the system.
- Fix the file system.
- Exit the emulator.
- Create a new extract file
./mfm_util --emulation_file ../c900.emu --extracted_data_file ../c900.extract
To fix your image via other binary tools and then recreate the emulator file:
./ext2emu --extracted_data_file c900.extract --emulation_file c900.emu --cylinders 612 --heads 4 --format Intel_iSBC_214_512B --quiet 0
Write out image file to a real hard drive:
You need to change the mfm_read-00C0.dts file to do any writing as it is set up for reading to begin with. What I did was create a copy of the file for reading and a second copy of the modified file for writing and I copy to correct file when reading or writing. I did this so I knew which file I was working with and when I write to a disk, I run the same procedure.
Do this once:
cp mfm_read-00C0.dts mfm_read-00C0.dts.read
cp mfm_read-00C0.dts mfm_read-00C0.dts.write
Modify the mfm_read_00C0.dts.write file:
Comment out this line (add the // to the beginning)
0x190 0x07 // OUT P9_31 = gpio3_14
//0x190 0x07 // OUT P9_31 = gpio3_14
Uncommented this line from:
//0x190 0x2d // OUT P9_31 = pr1_pru0_pru_30_0
0x190 0x2d // OUT P9_31 = pr1_pru0_pru_30_0
With these two files, you can copy the read or the write file to mfm_read-00C0.dts depending on what you are doing.
To now write a file to a read hard drive:
cp mfm_read-00C0.dts.write mfm_read-00C0.dts
./mfm_write --emulation_file ../c900.emu --quiet 0 --drive 1
cp mfm_read-00C0.dts.read mfm_read-00C0.dts
A couple of notes:
- Whenever I try to write to a physical hard drive, my process hangs on the first attempt. You need to ctrl-z the process and then use kill %1 to kill it.
- I write the “read” file back after I do my hard drive writes so I don’t forget and I shutdown the emulator.
To copy a file from your MFM Emulator to a USB memory stick:
mount /dev/sda /mnt
cp c900.emu /mnt