john@hp-pcd.UUCP (john) (04/19/86)
<<<<< < < > Has anyone with a V-20 processor used an 8087 with it? Do they work > together without contention? What kind of speed advantage did you > find? I have become addicted to an 8 Mhz 8088/8087 but like the > idea of CP/M native code with the new patch programs. How well do > THEY work? < One potential problem when running a V20 in 8080 mode is that the 8087 is still watching the instruction stream to see if any floating point instructions are being executed. I haven't checked the opcodes but I think you could probably find some 8080 opcodes that will send an 8087 out to lunch. John Eaton !hplabs!hp-pcd!john
davidsen@steinmetz.UUCP (Davidsen) (05/01/86)
In article <13600006@hpcvla.UUCP> john@hp-pcd.UUCP (john) writes: >< >> Has anyone with a V-20 processor used an 8087 with it? Do they work >> together without contention? What kind of speed advantage did you >> find? I have become addicted to an 8 Mhz 8088/8087 but like the >> idea of CP/M native code with the new patch programs. How well do >> THEY work? >< > >One potential problem when running a V20 in 8080 mode is that the 8087 >is still watching the instruction stream to see if any floating point >instructions are being executed. I haven't checked the opcodes but I think >you could probably find some 8080 opcodes that will send an 8087 out to >lunch. > >John Eaton >!hplabs!hp-pcd!john I don't think this is quite how it works... after reading my Intel manual and talking to a few hardware gurus, it appears that the coprocessor opcodes are flagged and passed to the 8087 by the 8088, rather than the 8087 "watching for" them. The 8088 will support up to three coprocessors, allowing use of things other than the 8087. In real life I have run a V20 for about a year without incident, using the special opcodes. My 8087 has yet to notice. If some hardware heavy can expound more, please do so, all I know is what I read and what works. Although there are handles for up to three coprocessors, I have never heard of anyone running more than one 8087, although there is the bus processor used to go between the 80186 and an 8087, and some type of i/o coprocessor, too. -- -bill davidsen seismo!rochester!steinmetz!--\ / \ ihnp4! unirot ------------->---> crdos1!davidsen \ / chinet! ---------------------/ (davidsen@ge-crd.ARPA) "Stupidity, like virtue, is its own reward"