7 Apr
2015
7 Apr
'15
5:13 a.m.
[...]
Now, a total imaging of one RL disk to another is not something you
should do. That would replace the pack serial number, in addition to the
issues with the bad block lists. Not to mention that different packs
have bad blocks in different places.
I agree. You're right that the best way to copy a pack is to load up the appropriate
OS in the simulator and instruct it to do the work. Because it has knowledge of the
filesystem, it will copy around bad blocks, identify new ones, etc. without stomping on
the serial number and factory recorded bad block data.
Sp, to get to the meat of it. No, bad blocks are not
replaced, or mapped
away, or faked. The drive and controller can detect bad blocks, and when
you try to read one, you'll get an error back. Drivers try a few times,
and then give up, giving an error back to the user program.
You should not try anything different.
[...]
Johnny
I will have to patch SIMH to support this paradigm because right now it expects the
backing store for its virtual RL02s to be readable at all times. IO errors trying to
access the underlying "file" halt the simulator. Additionally, there is no way
to report what type of error occurred via USB mass storage, only that fewer blocks were
returned than expected.
I think I'll need to have two completely different modes of operation.
A USB Mass storage mode would use the pack like a modern hard disk. The controller would
hide and internally use the last track for bad block identification and not expose it to
the PC. Also, the controller would hold some number of sectors in reserve, presenting a
flat, error free ~9.8MB disk to the PC. This would work for modern filesystems but be
completely useless for SIMH and physical computer compatibility.
The other mode will need to be a non mass storage interface like bulk or CDC mode
specifically for use with SIMH and any custom diagnostics. SIMH (after modification)
would then be able to access all the raw data on the pack and have access to any errors
that occur, handling them however it wants. Copying packs would need to be done just like
it is now, except in the simulator. You either mount or image and mount the first disk,
load your favorite OS in SIMH attached to the physical drive, and instruct it to copy disk
1 to disk 2, letting it copy around bad blocks in the manner it always has (preserving
compatibility).
Christopher