17 Jul
2014
17 Jul
'14
4:57 p.m.
On Wed, Jul 16, 2014 at 05:13:24PM -0600, Kevin Keith wrote:
There are a few open FPU cores floating around,
although adapting
them to use VAX floating point format might be rather difficult.
In the early days of microprocessors, FPUs were a large enough chunk of
circuitry that sometimes it was only feasible to have it as a coprocessor --
and fallback to software emulation if it wasn't found.
If I were to undertake such a project, that's the way that I would go.
I suppose it depends on how "authentic" you really want to be :-)
And, a big hack around dealing with I/O would be just to read and write data
to a memory space shared with a host PC. I have an ISA bus prototype card
sitting around (unused of course!), I don't know if there are such things
for modern PC busses.
But clearly you have to have the front panel :-)
One dream project would be to have a (replica?) PDP-11/20 front panel
hung on the wall, fully operational with Xilinx + flash (for its code) +
an SD card to emulate the core.
Anyways, that's what I would do if I had the time, and remembered
whatever I did with Xilinx stuff 20+ years ago.
mcl
p.s. if anyone *has* an 11/20 for sale, please contact me off-list :-)
It was my second "hands-on" marchine.
p.p.s. yes, I *am* that old.