doug@ross.UUCP (doug carmean) (05/24/89)
In <3390@orca.WV.TEK.COM> Andrew Klossner write (in response to my posting) >An MMU is not a "device," to be "driven" easily by a single module. >Big MMU differences cause ripples throughout the kernel, and in extreme >cases can affect user code. Notice that my posting stated that a "well written operating system requires a change to a single driver...". By well written I was referring specifically to SunOS, which requires very minor modifications to be ported to a new MMU. All of the code specific to the MMU is localized in a single routine, not scattered throughout the kernel. A new MMU will not affect user code even in the extreme cases. -- -doug carmean ross!doug@cs.utexas.edu -ROSS Technology, 7748 Hwy 290 West Suite 400, Austin, TX 78736 -Don't let my sarcasm fool you: I have no sense of humor.
haahr@phoenix.Princeton.EDU (Paul Gluckauf Haahr) (05/25/89)
in article <232@ross.UUCP> doug@ross.UUCP (doug carmean) writes > In <3390@orca.WV.TEK.COM> Andrew Klossner writes > >An MMU is not a "device," to be "driven" easily by a single module. > >Big MMU differences cause ripples throughout the kernel, and in extreme > >cases can affect user code. > Notice that my posting stated that a "well written operating system requires > a change to a single driver...". By well written I was referring > specifically to SunOS, which requires very minor modifications to be ported > to a new MMU. All of the code specific to the MMU is localized in > a single routine, not scattered throughout the kernel. A new MMU will > not affect user code even in the extreme cases. this is untrue even for sunos. to accomodate the new mmus for the 3/80 and sparcstation, sun has different kernels for the new machines. new versions of the operating system provide the -k flag to arch which will print sun3 and sun4 for old machines and sun3x and sun4c for new ones. libkvm.a runs different code to grub through the kernel depending on which mmu is used, and i believe different versions of ps and friends are needed for the different kernel architecures. the hat layer in sunos 4.0 does provide some distance between the mmu and the rest of the kernel, but some decisions are pervasive. for example, the layout of the u area is affected by the size of page tables, which depends on the page size. some user code is sensitive to machine page size, sometimes for performance, sometimes for functionality. paul haahr haahr@princeton.edu princeton!haahr