FPGA VAX update

Chuck> What surprises me about the home-built computers from scratch Chuck> is the lack of imagination when it comes to architecture. Chuck> Most are basically one-address-cum-accumulator designs. It Chuck> would seem that larger register files are much easier to build Chuck> nowadays and would open up the door to some 2 and 3-address Chuck> designs. Chuck> I've always thought that 24 bits is a nice word size for a Chuck> small computer. Divisible by 2, 3, 4, 6, 8 and 12 bits. An Chuck> instruction could use 6 bits for opcode and 3 register Chuck> addresses out of a 64 register file... Some Philips minis had 24 bit words. I worked on one, can't remember the model number. P2400? P9200? Psomething anyway. It had 8 sets of 8 registers, one for each interrupt level, so there wasn't any context saving overhead. No interrupt vectors either; you'd simply load the interrupt handler start address into the PC of that level. But still, a boring architecture by your definition: registers plus one memory address, plus an index bit. If you're going to go the 3 address route, it sounds like you're well on your way towards reinventing the CDC 6000 architecture. And of course that would be a fine thing to do -- if you're going to explore computer architectures, what better path to take than the one first walked by the foremost computer architecture genius of the 20th century? paul