[libre-riscv-dev] chinese sponsor, looking to design an ECP5-based dev board

[Samuel Falvo II]

On Mon, May 6, 2019 at 5:44 AM Luke Kenneth Casson Leighton
<lkcl at lkcl.net> wrote:
> this would allow us to use one of the FPGAs as a "peripheral" chip and
> the other(s) as the main CPU.

This is exactly how I intend on building out the Kestrel-3 today,
except substituting iCE40HX8K chips for the ECP5K family parts.  One
chip holds the CPU; a custom interface (which I call ByteLink) that
bridges to a second iCE40HX8K chip for access to video, audio, etc.
over a pair of PMOD ports; two UARTs[1]; the flash ROM adapter; the
static RAM adapter; and a timer to implement mtime/mtimecmp with.  If
I can fit it, a DMA controller to automate I/O to the mass storage
UART.  The second chip contains the aforementioned video interface,
audio interface, access to more RAM, and so forth.

________
1.  One UART is for the debug terminal, and minicom on the host PC
will talk directly to it until I can get the 2nd FPGA running with a
video interface.  The other is intended to provide access to
PC-/Arduino-hosted mass media (if you remember how Commodore and Atari
8-bit disk drives were handled, same idea).  However, I've toyed with
the idea of replacing this second UART with another ByteLink port
which would in effect memory-map attached peripherals, greatly
simplifying both software and the DMA controller.  However, I don't
know if I'll have enough room.

> thoughts appreciated, particularly if people believe this may be a
> saleable product (nothing to do with the Libre RISCV SoC itself)

If this board existed, and was be licensed under an open hardware or
copy-left license[2], and the price was affordable to me, I'd buy one
tomorrow.  Especially if options could be had to help manage the cost
to the interested hobbiest (e.g., choice of 2, 3, or 4 FPGAs, for
example; choice of how much RAM, etc.).

I'd want the board to be copyleft licensed, though, so that I could
have the right to make the changes I'd need for the Kestrel project.
For example, removing peripherals that aren't used and adding a
backplane expansion bus, thus basically turning the board into the a
motherboard for the Kestrel.

________
2.  Fun fact: I'm not a copyleft purist for everything that I use;
but, after being burned, I now firmly believe that all the
software/hardware components required to actually use a device should
be licensed under a copyleft-type license.  Most hardware very much
falls under this category, including what one would consider to be a
"motherboard."  Put simply, ask yourself this question about any
software or hardware component: is it required for the device to
operate as intended in at least some minimal configuration?  If the
answer is yes, then it must be copyleft.  Value add-ons?  Perhaps not;
it depends.  But for core functionality?  Absolutely.

-- 
Samuel A. Falvo II