meulenbr@cstw01.UUCP (Frans Meulenbroeks) (01/24/89)
Hi! Apologies for the PC readers of comp.os.minix. This is not appropriate for them. There has been some discussion about minix running on a 68020 and st's with this chip. I'd like to drop my knowledge here, for who is interested: It is possible to add a 68020 to an ST. I've built the setup as described in the German mag. C'T. Basically this means generating your own E/VMA/VPA and some juggling with DTACK and AS. There is some motorola application note on this topic. Sorry, I don't have the number handy. It is called something like: Evaluating a 68020/68881 in a 16 bit platform. By adding the 020 into an ST hardly any gain is obtained. This is caused by the fact that bus cycles are still 16 bits and need 4 clock cycles. In some occasions the speed even decreases (on 8 mhz). The only gain obtained is from the cache and the 68881 (if you have a compiler which supports it). This system will not run an unmodified TOS. Heavy patching is needed to get TOS running. However, the system has no problem running minix. There is only one small change needed: The minix bootstrap code in bootblok.s uses bios calls to load minix. A boot loader which does DMA directly cures this. For those who are interested: I have a very dirty one. Once again: Do not expect a big speed increase. Something about 20 % would be quite good. I am currently trying to convince the board to run at 16 Mhz (picking even more wait states). However my setup still crashes occasionally, and also here the gain is not tremendous. If you want to obtain real gain local memory should be added to the board. There are provisions to do so, and then the gain can be around 5 or so (given 32 bit mem on 16 Mhz, no wait state, 3 clock/bus cycle) However, this will require some minix hacking, since one then cannot DMA to this local memory. I intend to tackle this once I get the system running at 16 Mhz, and memory is becoming a little cheaper again. Of course one also can wait for the longly rumoured TT which will run S5R3 (Unisoft port), according to my sources. -- Frans Meulenbroeks (meulenbr@cst.prl.philips.nl) Centre for Software Technology ( or try: ...!mcvax!philmds!prle!cst!meulenbr)