TU58 tape issues

Thanks for the suggestions. As an update, I've done a little more investigating. I ended up installing tu58em and verifying that the tape image was good and that I could boot using tu58em. Last night, I did a dump of tu58em's debugging output and manually issued the same set of reads to my emulator. I verified that all the packets had the same checksums, the same first few and last few data bytes, and that the end packets all matched. So it's looking like it's coming down to either something related to timing or there's something I'm not doing right with respect to breaks or inits. In looking over the RT-11 boot code, I'm now pretty sure that things break down when it shifts the monitor uses. I"m thinking my next step is to interpose a machine with 2 serial ports and record the whole protocol when it fails and see if that shows anything. BLS