On 10/4/20 1:50 PM, J. David Bryan via cctalk wrote: > On Friday, October 2, 2020 at 13:51, Al Kossow via cctech wrote: > >> Those would already be broken with Bob's use of large negative numbers >> for physical end of tape and 'bad block is here' (you don't get to know >> how big that bad block was, so that is hell with tapes with >> variable-length records, grumble..) > > I'm not sure I understand. SIMH metadata markers are treated in the tape > library code as unsigned values, so EOM and erase gap are seen as large > unsigned values. The format limits record lengths to 24 bits (so about 16 > MB maximum per record), reserving the upper 8 bits to indicate the type of > the marker, and the bad record marker is the top byte = 0x80. The record > length of a bad block is encoded in the lower 24 bits and indicates how big > the bad block was. > > What am I missing?
I don't believe that you're missing anything. When I process these files, I mask off the lower 24 bits as the block length. A 16MB tape block is impossibly large in any case. --Chuck
