From: ron@ronnatalie.com (Ronald Natalie)
Subject: [TUHS] pdp11 UNIX memory allocation
Date: Tue, 6 Jan 2015 17:36:46 -0500 [thread overview]
Message-ID: <50E11A72-348F-4391-B444-33DD1B4ED1CC@ronnatalie.com> (raw)
In-Reply-To: <54AC5F94.3080401@update.uu.se>
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Another quaint bit of history was when we made the jump to actually running the kernel in split-I/D mode. My good friend Joe Pistritto wrote the JHU boot loader for that. The 512-byte boot loader that was the standard UNIX one was used to load Joe’s split I/D booter. It had a better support of the UNIX file system, but the question was how do you get from a non-split I/D program into the split I/D program. Joe’s solution was rather clever. He put an instruction that stored the processor status word with the new kernel mode at the top of the boot loader’s address space. As he did the store the PC rolled over and now it was running at the new mode at location zero.
Years later I found that others had solved the problem by just setting up the kernel registers and executing a trap which switched the modes. I always thought Joe’s solution was more elegant. The kernel started the same way any other UNIX program would start.
next prev parent reply other threads:[~2015-01-06 22:36 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.149.1420581544.3354.tuhs@minnie.tuhs.org>
2015-01-06 22:20 ` Johnny Billquist
2015-01-06 22:36 ` Ronald Natalie [this message]
2015-01-06 23:14 ` Johnny Billquist
2015-01-07 2:39 ` John Cowan
2015-01-07 2:59 ` Johnny Billquist
2015-01-07 2:18 Noel Chiappa
2015-01-07 16:17 ` Clem Cole
[not found] <mailman.151.1420584979.3354.tuhs@minnie.tuhs.org>
2015-01-06 23:34 ` Johnny Billquist
2015-01-06 23:52 ` scj
2015-01-07 16:14 ` Clem Cole
2015-01-07 17:27 ` Dave Horsfall
-- strict thread matches above, loose matches on Subject: below --
2015-01-06 22:45 Noel Chiappa
2015-01-06 22:55 ` Clem Cole
[not found] <mailman.147.1420574271.3354.tuhs@minnie.tuhs.org>
2015-01-06 20:20 ` Johnny Billquist
2015-01-06 20:33 ` random832
2015-01-06 21:57 ` Ronald Natalie
2015-01-06 22:00 ` Clem Cole
2015-01-06 22:04 ` Ronald Natalie
2015-01-07 1:46 ` Dave Horsfall
2015-01-07 2:00 ` Ronald Natalie
2015-01-07 6:29 ` Dave Horsfall
2015-01-07 6:39 ` Warren Toomey
2015-01-07 10:06 ` Brantley Coile
2015-01-07 13:29 ` Jacob Ritorto
[not found] ` <CAC20D2PP1hGyYsep1yNtj9KO55a-V02+QHS+S7bX-4joJy222g@mail.gmail.com>
[not found] ` <1420583703.863814.210431037.61D6C6EC@webmail.messagingengine.com>
2015-01-06 22:36 ` random832
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