WOW !
I can read from the mass storage. DIR is working and various READx commands are working too. Finally, I was able to load some files from swap LIF images which I downloaded from hpmuseum FTP site. :-)
It took me five days (ok, four days, yesterday I was building the Clonix module and I was playing with various ROMs) to nail a stupid bug which was based on my misunderstanding of correct behaviour of IL unit after receiving the NRD command.
But everything bad is good for something else. When I tried to find the bug, I completely rewrote my spaggetti code of HP-IL communication routine and now, it is nicely structured, according to HP specification ("Firmware Design for HP-IL devices" appnote), source is commented etc.
Now, I just need to clean several minor bugs and I can concentrate on the writing to MMC part.
I hope that I will finish it before my wife will kill me. I hate the questions like "Why are you playing with the old calculator the whole evening ?" or "Do you think that you will have time tomorrow ? You promised, that you will go to the theatre with our daughter and also, I need to talk with you a bit." etc.