🚀 go-pugleaf

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