[J-core] Sega saturn retrocomputing.

Christopher Friedt chrisfriedt at gmail.com
Tue Jul 19 09:55:30 EDT 2016

On Jul 18, 2016 11:51 PM, "Rob Landley" <rob at landley.net> wrote:
> FYI:
> http://hackaday.com/2016/07/11/cracking-the-sega-saturn-after-20-years/

I think I sent a link on the ML to the YouTube video about a week ago.

> (Alas, when we looked at possibly doing an FPGA saturn clone with J2 as
> a side project for the 20th anniversary, it turned out there were some
> tight timing constraints that make games misbehave very easily, at least
> in software emulation. I think some j2 instructions take different
> numbers of clock cycles than sh2 did? Don't remember the details, but we
> shelved the idea...)

I'm still interested in doing some Qemu work. Currently the SH core (even
before J2 additions) is not cycle-accurate, which is a bit of a critical
error made by the initial Qemu SH port. Bill Gatliff's tests highlighted

Emulated peripherals are not likely to be cycle accurate, but more
importantly, simultaneously running CPU's with tightly coupled timing
requirements is almost guaranteed to be cycle inaccurate, as there is no
efficient means of "clocking" them synchronously using Qemu's method of
emulation (binary translated & cached blocks).
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