Date: Tue, 8 Mar 2016 15:09:30 -0800 From: John Clark <jeclark2006@aim.com> To: Markus Hitter <mah@jump-ing.de> Cc: freebsd-embedded@freebsd.org Subject: Re: ? about kernel size.. Message-ID: <938133EE-CCEE-4F08-BB78-8227D9D0C6EC@aim.com> In-Reply-To: <56DF513E.9000405@jump-ing.de> References: <CAPKZHbVyPji-bZwDzM77TN6qybjRcf%2BZe5r6WZmbG98LkhT-rg@mail.gmail.com> <CANCZdfriqr24Lh9ZuptaC0gEm6gAV6LN9XHcVAJtbyaBejEgNg@mail.gmail.com> <CAPKZHbW%2BG7WnSU__yeYBVPqs8MPmFm-5q_wM4sm9FxHhEEgPDg@mail.gmail.com> <1457473674.1406.46.camel@freebsd.org> <CAPKZHbX8BXKC_=8PPvtasqE%2BRj96_mPQkqdRt=hqU6fazxpPfA@mail.gmail.com> <56DF513E.9000405@jump-ing.de>
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Not to barge in to your discussion=85 but yes there were Unix variants = that worked on the 286. Xenix was one such OS. Xenix being Microsoft=92s = idea of avoiding the Unix name=85 Originally Xenix ran on PDP-11, and was ported to other machines that = have long passed into the oblivion of technological Hell. As for =91preemetive multitasking=85 of course one can run a preemptive = scheduler on almost any CPU that has a clock interrupt. I wrote one for the 286 based on the kernel described in Douglas Comer=92s= =93Xinu=94 book. Products with that hack where produced for about 8 years=85 in the = early-mid-80s. I wrote it such that it would run in a DOS box and allow = for machine control of various robotic systems for industrial inspection = machines. In any case one can develop a multitasking kernel to run in a non-MMU = based system=85 just lends itself to crapping out on the least = provocation=85 What an MMU provides is hardware =91address translation=92 such that the = application can run in an =91virtual absolute=92 addressing space, have memory protection such that errant code can=92t clobber other tasks = or the kernel, and also given appropriate devices, have =91swapping=92 for larger than real memory applications. The 286 =91segment=92 registers gave a bit of =91translation=92 = capability in that one could address relative to the segment registers, = and so, code and data could be place in available member and context = switched would update the segment registers. The segment registers were a crappy way of accessing memory if one had = long linear arrays of data to process=85 such as image processing=85 = which happened to be the application of my work at the time=85 And one could always implement an external MMU which was popular with = the Motorola M68K which was sort of the contemporary alternative to the = Intel x86 line. John Clark. On Mar 8, 2016, at 2:25 PM, Markus Hitter <mah@jump-ing.de> wrote: > Am 08.03.2016 um 22:56 schrieb Brad Walker: >> But, are you saying that no engineering has been done on this yet OR = no >> amount of engineering could make it work? >=20 > If I recall correctly from some 25 years ago, memory address mapping > (which is what a MMU does) is mandatory for preemtive multitasking. An > i286 can't run a Unix-like OS either. >=20 >=20 > In 2008 I tried to get FreeBSD down to its minimum, too. The success > post is about all what's left today: >=20 > = https://lists.freebsd.org/pipermail/freebsd-embedded/2008-October/000604.h= tml >=20 > The task to get there is simple and straightforward, but time = consuming: > go step by step through the kernel configuration to disable whatever = you > can spare. Configure, build, try, repeat. If you need a small entire > system, do the same for packages and every single file you copy into > your system image. >=20 >=20 > Markus >=20 > --=20 > - - - - - - - - - - - - - - - - - - - > Dipl. Ing. (FH) Markus Hitter > http://www.jump-ing.de/ > _______________________________________________ > freebsd-embedded@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-embedded > To unsubscribe, send any mail to = "freebsd-embedded-unsubscribe@freebsd.org"
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