DAN@mit-ml.arpa (03/19/83)
From: Dan Blumenfeld <DAN@mit-ml.arpa> Some new info for those interested in MPX-16 boards... Originally, MicroMint was going to supply the CBIOS for CP/M-86 in EPROM, so that a stock version of CP/M-86 from DR would boot... well, things have changed. They realized that this was a very bad move if they also wanted to run MSDOS, so now all you get on EPROM (one 2732) is a generalized Booter, which will initialize the board and read in the system tracks on the diskette. They also give you the listing for the Booter, which happens to be written in Intel's PL/M. I'm not sure if it is the complete listing, because the Booter initilaizes the 8272A Disk Controller for a 5 1/4" diskette, but MicroMint claims that the Booter will also work with 8" drives. In any event, what this means is that you have to purchase CP/M-86 from MicroMint. The 5 1/4" version is available now, and the 8" version will be available by the end of March. I talked to one of the technical people there, and they assured me that the CBIOS source would be included on the diskette (it better be!). Two other minor but useful additions have been made to the board. The address map PROM is now included with the kit, so that you don't have to burn one yourself. The board also comes with nine expansion slots in place, rather than the advertised five. One of the problems with booting CP/M-86 is that the entire OS can't fit on the system tracks of a standard diskette. What happens is that the Booter reads in a smart Loader from disk. The Loader locates the CP/M-86 proper on the diskette (ideally by looking for the file CPM.SYS in the directory), reads it in, and cold boots. The problem with this is that that all the user tracks on the diskette are skewed, so the loader has to know about this. In many systems, the Loader assumes that the CPM.SYS file is right after the directory (i.e. the first file on the diskette), which simplifies the Loader's job, but is a gross solution. This is how MicroMint does it. I'm planning on doing one of two things to alleviate this problem. One idea is to make track zero on the diskette double density (normally it is single). Since track one is double density on a DD diskette, this should be enough room for the entire CP/M-86 system. A second possibility is to place the entire CP/M-86 in EPROM, as four sockets are available on the MPX-16. The "booter" would simply initilaize the system, then copy the OS from EPROM into RAM, and then cold boot. Either solution requires modification of the Boot EPROM. MicroMint can only provide this on an Intel ISIS diskette in PL/M, but fortunately we have a Intellec III development system here at UPENN. Suggestions and comments on this? Dan