[Simh] Problem with reading tape with PDP-11 SIMH

[Al Kossow]

On 5/21/15 7:55 PM, Timothe Litt wrote:

> This is incorrect.  A tape mark is 32-bits of zero.  0x80000000 is an invalid encoding and should be reported as
> a format error.  (It indicates a length of zero with an error, but the record length field must be non-zero.)
>

This is what you get if the tape drive has a read error, but returns no data, which is generally what happens on
SCSI tape drives, and points out a serious problem with the format when you are dealing with reading tapes with bad blocks.

There is nothing in the format that gives any hints what the tape drive did when it hit a bad block, and different drives
do different things. Some return nothing, some return the bad data, some retry the blocks returning data on every retry,
some don't.

My program keeps a text log which I include if an image I make has bad blocks in it, but I never wrote out the scsi ident
string of the drive in it.