saare@ibmpa.UUCP (John Saare) (01/04/89)
Sorry I couldn't find the reference to Leo's note asking about the Acorn. Hello Leo. I'm using the Acorn in a small EFIS for experimental aircraft. I chose it because the Acorn chip set integrates a great deal of function in a "commercially available" small number of parts, as opposed to those used by C-A, Atari, etc.. The parts are sold by the original mfgr and second sourced by VLSI in Arizona. A complete Acorn system can be built by essentially connecting the dots, i.e., no buffers, decoders, counter, mux/demux, just add memory and go! The architecture is, well, unusual. Like most RISC's, it's 32-bits throughout. Not being a CPU guru, it's difficult for me to say whether the machine offers the right blend between performance and cost, or that the architecture is even competent. There's 16 32-bit registers. Depending on mode of operation, some of these registers are "bank switched" to save interrupt latency. A possibly wasteful feature is that EVERY instruction is conditional, which I'm sure simplifies circuitry but wastes an awful lot of instruction space (well, it is a RISC). There are no provisions for compilers to optimize against cache misses because there's no cache. The CPU is closely coupled to the memory controller/manager, which is optimized for page-mode DRAM operation. In fact, all parts in the family are closely coupled to the the memory controller/manager(MEMC). I don't remember certain numbers off hand, but I believe the largest virtual address space SUPPORTED by the MEMC is something like 32Mb with 16K(?) pages. Any TLB operations must be done entirely in software. For my application, I don't care, as there'll be no backing store for virtual memory anyway, so there'll be no virtual memory. I'll be using the page-faulting mechanism strictly for process separation enforcement (OOOOooooooo, that sounds painful). VLSI makes available a PC-DOS cross-development system, C-compiler, assembler, etc. The parts in the family are: VL86C010 - CPU VL86C110 - RISC Memory Controller VL86C310 - Video Controller (Don't worry Amigoids) VL86C410 - I/O Controller VLSI seems very helpful when it comes to providing speed and temp spec'd parts. I'll make no claims regarding performance, other than, yes, it's A LOT FASTER THAN a 7Mhz 68000. Sorry to ramble, but I hope this answers some questions. YHOS -- John Saare