Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!microsoft!brianw From: brianw@microsoft.UUCP (Brian WILLOUGHBY) Newsgroups: comp.sys.apple2 Subject: Re: Multitasking on a II Message-ID: <60236@microsoft.UUCP> Date: 3 Jan 91 02:32:09 GMT References: <10806@ucrmath.ucr.edu> Reply-To: brianw@microsoft.UUCP (Brian WILLOUGHBY) Organization: Microsoft Corp., Redmond WA Lines: 43 In article <10806@ucrmath.ucr.edu> rhyde@ucrmath.ucr.edu (randy hyde) writes: >>>> All 65x02 instructions are uninterruptible. > >This is true for the 65x02, but not the 65c816. The 65c816 as the >/abort pin which can interrupt an instruction on any given clock >cycle, not just an instruction fetch. As mentioned earlier, uninterruptible >instructions don't stop DMA (e.g., multiple processors like a MILL, Softcard, >or other coprocessor) from munging data between clock cycles. I thought we were talking about the Apple ][ in this thread? To multitask or not to multitask, that is the question. None of the Apples use the ABORT pin, so it is totally ridiculous to mention it here except, perhaps, as an exercise in developing new hardware around the 65c816 (which would make a very interesting alternate thread, I'll admit). I wouldn't consider the loss of the use of my CPM card (which isn't even plugged in now) a serious drawback if it's DMA prevented multitasking. The truth is, there is nothing (but software development) preventing multitasking in the ][. >Why not just use the SEI instruction to prevent entrance into a critical >section? > >On cheap systems you can do this. An error in the program (i.e., forgetting >to turn the interrupts back on) could destroy the multitasking system though. The key issue is that you can do it. Most of the critical sections would be in the operating system code (if my assumptions are correct), so once the multitasking system were debugged, general development would not be affected by this minor imperfection. >>> Poorest interrupt latencies in the known market. > >... It handles interrupts rather well. >*** Randy Hyde Thank you for your support. At least the advantages of the 6502 can be mentioned alongside its deficiencies. Brian Willoughby UUCP: ...!{tikal, sun, uunet, elwood}!microsoft!brianw InterNet: microsoft!brianw@uunet.UU.NET or: microsoft!brianw@Sun.COM Bitnet brianw@microsoft.UUCP