Post by Roberto Waltman
I have been thinking about implementing something like the Lilith in
an FPGA, as a way for me to learn about FPGAs, Verilog/VHDL, etc.
The "something like the Lilith" is not defined yet. Candidates are the
Lilith, a Lisp Machine, the Xerox Alto (if I can find enough
information) and the Harris RTX-2000 Forth processor (if I can find
software that runs on it)
I something think along similar lines, but such a project is a major timesink, and in the end will not yield a major advantage over Emulith.
In case of the Lilith / Medos combo there are several issues to solve :
Lilith's microcode is intrinsically linked to the propriertary HB D120 cartridge diskdrive. You will have to rewrite the microcode for that part. I intend to do that anyhow, so I can one day run my real Lilith from an IDE disk .
Also the video circuitry is not compatible with anything modern, a redesign is needed.
The RAM access is complicated, with 64-bit wide reads and 16 bit wide read/writes.
And i will not mention the RAM muxing via priority encoders....(the Lilith has freerunning DRAM refresh )
On top of that Medos does not have a hierarchical file system ( 1979 you know...)
Wading through 100's of files gets tiresome rather quickly.
On the plus side :
The actual CPU is probably the easiest part, Emulith should give you a pretty good idea on how it works.
Schematics for the Lilith are on my FTP-site, both the "official" ETH ones ( with bugs..) and my reverse-engineered ones, probably with their own set of bugs.. ( Eagle CAD format ).
And there is of course plenty of software available.