I was in the middle of working with this with Konstantin when COVID
stopped everything.
We had just changed the crystal from 20MHz to 18MHz (as I recall) so
that the RAM could run with a single wait state. I was implementing a
bootloader that would reside on-chip. It would copy programs from
serial to SPI FLASH. Then, at reset, it would copy the program from SPI
FLASH to RAM and run from RAM. So, the 18MHz crystal should actually
give better performance when running from RAM.
That was almost working when worked stopped. But performance was
awful. Too awful to be the slow chip so I think something was set up
wrong (or maybe the SPI was just very slow. Never really dug into
that.) The code is still set up to use the 20MHz crystal.
By the way, when I say that the eZ80 is one of my favorite chips, I
meant the eZ80F91. The stock Z20X has an eZ80F92 which is not as
capable. It has fewer peripherals (no Ethernet for example) and, worst
of all, no PLL. So it is limited to the crystal speed. The eZ80F91
usually uses something like a 4-5MHz crystal with the PLL configured to
run at 50MHz. Given that it is SISC, that really performs pretty well.
Knivd has a daughter board that can be used to replace the eZ80F92 with
the faster eZ80F91:
https://www.pcbway.com/project/member/?bmbno=4582C8E5-A4FF-44 . He also
has z380 and Zneo daughter boards. The Zneo is supported by NuttX (as
z16f), but the z380 is not.
On 2/20/2021 1:34 PM, Brennan Ashton wrote:
I saw that Greg had started initial support for this retro computer a
year ago and I was curious if anyone else has experience with it. I
was considering doing a board run and building one for myself and
would be happy to build a few if there are people interested since I
will have to order multiple PCBs anyway.
https://z20x.computer/
Greg, are you still doing anything on this? I know you have had
interest in the past with it.
It looks like there has been some renewed interest in the Z80 with
Byron integrating the clang port.
--Brennan
