car@trux.UUCP (Chris Rende) (02/14/91)
I've noticed that the 3b1 can only access one disk at a time. I.e., during floppy disk accesses the hard disk is idle - and vice versa. (Especially evident during floppy formatting). However, I've seen references to seperate HD and FD controller chips. I suspect that there is some common circuitry between the HD and FD interfaces which prevents them from operating independantly. (IBM PC clones have seperate controllers which can work independantly - 3b1's don't seem to have that luxury). Is this true? car. -- Christopher A. Rende Central Cartage (Nixdorf/Pyramid/SysVR2/BSD4.3) uunet!edsews!rphroy!trux!car Multics,DTSS,Unix,Shortwave,Scanners,UnixPC/3B1 trux!car@uunet.uu.net Minix 1.2,PC/XT,Mac+,TRS-80 Model I,1802 ELF trux!ramecs!car "I don't ever remember forgetting anything." - Chris Rende
botton@i88.isc.com (Brian D. Botton) (02/14/91)
In article <528@trux.UUCP> car@trux.UUCP (Chris Rende) writes: >I've noticed that the 3b1 can only access one disk at a time. I.e., during >floppy disk accesses the hard disk is idle - and vice versa. (Especially >evident during floppy formatting). > >However, I've seen references to seperate HD and FD controller chips. > >I suspect that there is some common circuitry between the HD and FD interfaces >which prevents them from operating independantly. (IBM PC clones have seperate >controllers which can work independantly - 3b1's don't seem to have that >luxury). > >Is this true? > Yes this is true. The common circuitry is the DMA address and data chips on the mohterboard. Those chips are single channel and thus cannot do transfers to/from two devices at once. This could be solved by putting a floppy controller in one of the expansion slots and giving it it's own DMA controller. Then the motherboard chips and the expansion chips whould just have to do arbitration, which is provided for. As it stands now there is no way to make the floppy and hard disks work together better. -- ... ___ *** _][_n_n___i_i ________ ******* Brian D. Botton (____________I_I______I_I_______I laidbak!botton or /ooOOOO OOOOoo oo oooo oo oo laidbak!bilbo!brian
thad@public.BTR.COM (Thaddeus P. Floryan) (02/14/91)
In article <528@trux.UUCP> car@trux.UUCP (Chris Rende) writes: >I've noticed that the 3b1 can only access one disk at a time. I.e., during >floppy disk accesses the hard disk is idle - and vice versa. (Especially >evident during floppy formatting). > >However, I've seen references to seperate HD and FD controller chips. > >I suspect that there is some common circuitry between the HD and FD interfaces >which prevents them from operating independantly. (IBM PC clones have seperate >controllers which can work independantly - 3b1's don't seem to have that >luxury). > >Is this true? The "Disk Bus Interface Unit" (both floppy and HD) are on the same DMA per the info I just read in the UNIXPC Reference Manual. Expansion boards and the 68010 itself are on different DMA channels. Reading pages 2-43 thru 2-44 indicates that one or the other disk can be transferring data at one time through the same DMA circuitry, so there's your "common circuitry" and the reason for the "problem." If some (external) disk controller could be plugged into an expansion slot, it'd be on its own DMA channel and, thus, not block the other disk(s); I'm not aware of any such external disk controller cards. The separate DMA channels also explains why expansion card operations don't (appear to) block disk access (fortunately! :-) Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]