treval@ace.UUCP (Trevor Luker) (05/22/86)
Hi Netland, I'm trying to figure out how to put a second processor (a 68008) onto the pc expansion bus in such a way that it can tell the 8088 to "shut-up" and then take complete control of the memory and peripherals. (This is to allow some experiments that I am doing with Xinu to run more easily (Xinu likes a nice linear address space)) I can think of two ways of doing this: 1). The software approach: Have a small amount of dual ported memory on the 68008 card used as a post box. send a message to the 68008 to force it to execute a halt instruction and await an interrupt before continuing. Force an interrupt on the 68008 from the 8088 and then immediately execute a halt instruction. This should force the 8088 to relinquish the bus allowing another "bus-master" to take over. (Is this so, are all buffers and drivers put into a tri-state condition?). What about interrupts from peripherals? can I stop these reaching the 8088?) When the 68008 has finished it's task, it can force an interrupt onto the 8088 to allow it to continue. 2). The hardware approach. Find a way from the expansion bus on the pc to issue a bus-request, wait for the corresponding bus-acknowledge, at which point the 8088 should have relinquished the bus allowing the 68008 to take over. 3). The very hardware approach Make a board containing both a 68008 and a 8088 with associated hardware to allow any one of the processors to have control of the bus at any one time. This "Hybrid" would replace the 8088. Each processor would be responsible (via software) for swapping over to the other processor when requested. Problems: Apart from the above mentioned problems, the following spring to mind:- 1). Who does the memory refreshing when the 68008 has control. 2). Is it really worth the effort? :-) If anyone has any clues as to how this would be possible, or knows of a product that is available the already does this, or knows of where I can the information from to answer the questions myself I would be very happy if they could send them to me. Thanks in advance, Treval -------------------------------------------------------------------------------- ACE Associated Computer Experts bv treval@ace.uucp NZ Voorburgwal 314, 1012 RV, mcvax!ace!treval Amsterdam, Holland. +31 20 26-24-00 --------------------------------------------------------------------------------