Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!leah!rpi!rpi.edu!deven From: deven@rpi.edu (Deven Corzine) Newsgroups: comp.sys.amiga.tech Subject: Re: MEMF_PHYSICAL? Message-ID: Date: 24 May 89 06:51:08 GMT References: <6914@cbmvax.UUCP> <6943@cbmvax.UUCP> Sender: usenet@rpi.edu Organization: RPI Public Access Workstation Lab, Troy NY Lines: 61 In-reply-to: thomas@cbmvax.UUCP's message of 22 May 89 13:43:38 GMT In article <6943@cbmvax.UUCP> thomas@cbmvax.UUCP (Dave Thomas QA) writes: In article deven@rpi.edu (Deven Corzine) writes: > The name MEMF_PUBLIC clearly implies a relation to memory protection > (more precisely, lack thereof) yet it isn't so clearly defined. > Clearly, it implies that other tasks can access the memory, (and that > much the RKM clearly states) but what isn't clear is what effect, if > any, such a designation should mean with regards to virtual memory. It has no effect on virtual memory. Public memory is simply memory accessible to all tasks. It has nothing to do with virtual memory at all. There is absolutely no reason why public memory could not be virtual memory. I understand completely. I simply passed along a claim this book made, and as such, felt compelled to at least TRY to argue the (undeniably weak) case for their position. > It COULD be interpreted as "any task can access the memory at any > time, so it must always be in memory." It could, but that's complicating the definition needlessly. Obviously, but it's how they seem to have interpreted it. Interrupt code MUST be in physical memory since interrupts must be serviced in a timely fashion. Also, interrupts on the Amiga do not really execute as part of any task and are in supervisor mode. Memory protection need not apply to them. Fine. But the RKM's say interrupt code and data MUST be in MEMF_PUBLIC memory. Why? Try to keep the concepts of memory protection and virtual memory separate in your mind. They really are two different animals. While it is true that systems which implement usually implement the other, it is not always the case. Memory protection is going to be very difficult to implement on the Amiga without breaking 99% of the programs out there, but virtual memory without protection can probably be done with much less impact on the software base. I fully understand the distinction between memory protection and virtual memory. I was just arguing a case which was lost from the start. And yes, virtual memory will have far less damaging effects than memory protection, with the design of the operating system -- the message passing mechanism, in particular. But that wasn't the point. Regardless, I give up. It wasn't MY idea in the first place, and I thought it was stupid, also. I simply passed it along for whatever (small) value it might have. Geez. Deven -- shadow@[128.113.10.2] Deven T. Corzine (518) 272-5847 shadow@[128.113.10.201] 2346 15th St. Pi-Rho America deven@rpitsmts.bitnet Troy, NY 12180-2306 <> "Simple things should be simple and complex things should be possible." - A.K.