From mboxrd@z Thu Jan 1 00:00:00 1970 From: cowan@mercury.ccil.org (John Cowan) Date: Sun, 28 Apr 2013 01:57:33 -0400 Subject: [TUHS] Need a new PDP-11 or VAX? In-Reply-To: <20130428035736.GA1001@bitmover.com> References: <20130427224146.GR664@bitmover.com> <20130428013911.GD24560@mercury.ccil.org> <20130428035736.GA1001@bitmover.com> Message-ID: <20130428055733.GH24560@mercury.ccil.org> Larry McVoy scripsit: > Ideally with 32 bit ints, 64 bit longs, 32 or 64 bit pointers in the > compiler, obviously more registers, and nothing like the vax. Sounds right. I'm torn between the 8 addressing modes of the PDP-11 and 32 registers, or the 16 addressing modes of the Vax and only 16 registers. In either case, 32-bit instructions allow all operands to have full addressing mode on both source and destination rather than just a register for one or the other. The byte/word bit of the memory instructions would become 2 bits for byte/short/int/long. One issue is whether to have a single 32-bit index in modes 6 and 7, or provide a full 64-bit index with two trailing 32-bit words. Branches can have much bigger offsets, which is good. The FPP needs a complete overhaul: it should look pretty much like the main ISA, and of course use IEEE format operands. Hmm, perhaps get *really* modern and use 3 bits of size for byte/short/ int/long/float32/float64/decimal64/decimal128, where the last two are IEEE 754:2008 decimal floating point values. > I'm too dumb to get it but I never warmed up to the vax. When I saw it had 256 opcodes I knew I was never going to master it, no matter how orthogonal it was. (I came from the PDP-8 to the PDP-11.) Little did I know the Last ISA would have thousands and thousands of opcodes! -- Note that nobody these days would clamor for fundamental laws John Cowan of *the theory of kangaroos*, showing why pseudo-kangaroos are cowan at ccil.org physically, logically, metaphysically impossible. http://www.ccil.org/~cowan Kangaroos are wonderful, but not *that* wonderful. --Dan Dennett on zombies