On Thu, Aug 12, 2021 at 5:29 PM Fritz Mueller <fri...@fritzm.org> wrote: > > > > On Aug 12, 2021, at 3:31 PM, Glen Slick <glen.sl...@gmail.com> wrote: > > If I translate the logical > > sector order RX-02 disk image back into a physical sector order disk > > image (dealing with track shifting, sector interleaving, and track to > > track sector skewing) then RT-11 on SIMH is happy with the disk image. > > Ah, interesting... Where's the best place to look for more information in > the RX02 RT-11 logical/physical mapping? > > Glen, if you wouldn't mind sending me a copy of your resulting > simh-compatible image, I'd be happy to post it in an upcoming blog article > for others who might find it useful as well... > > cheers, > --FritzM.
One bit of information that I found helpful as a reference when I looked at this quite a while ago was the 2.11BSD RX02 floppy disk device driver source code, which can be viewed online here: https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.11BSD/sys/pdpuba/rx.c In particular, the routine rxfactr(), which as the comment says it calculates the physical sector and physical track on the disk for a given logical sector. I used that as a starting point to write a simple utility to read an RX-02 disk image file in logical sector order and output an RX-02 disk image file in physical sector order. /* * rxfactr -- calculates the physical sector and physical * track on the disk for a given logical sector. * call: * rxfactr(logical_sector,&p_sector,&p_track); * the logical sector number (0 - 2001) is converted * to a physical sector number (1 - 26) and a physical * track number (0 - 76). * the logical sectors specify physical sectors that * are interleaved with a factor of 2. thus the sectors * are read in the following order for increasing * logical sector numbers (1,3, ... 23,25,2,4, ... 24,26) * There is also a 6 sector slew between tracks. * Logical sectors start at track 1, sector 1; go to * track 76 and then to track 0. Thus, for example, unix block number * 498 starts at track 0, sector 25 and runs thru track 0, sector 2 * (or 6 depending on density). */ static rxfactr(sectr, psectr, ptrck) register int sectr; int *psectr, *ptrck; { register int p1, p2; p1 = sectr / 26; p2 = sectr % 26; /* 2 to 1 interleave */ p2 = (2 * p2 + (p2 >= 13 ? 1 : 0)) % 26; /* 6 sector per track slew */ *psectr = 1 + (p2 + 6 * p1) % 26; if (++p1 >= 77) p1 = 0; *ptrck = p1; }
