Date   : Tue, 31 Jan 2017 16:19:48 +0100
From   : kortink@... (John Kortink)
Subject: Pi-based second processor - fast, flexible,

On Tue, 31 Jan 2017 14:40:47 +0000, Ed Spittles <percy.p.person@...>
wrote:

>On 31 January 2017@..., John Kortink <kortink@...> wrote:
>
>>
>> I'm curious however. How was the 274 MHz figure achieved and
>> calculated ? I can't find any satisfactory explanation for it
>> on the web page you point to. It seems rather high for a mere
>> simulation running on a 1 GHz processor, more so since the
>> Z80 then seems to lag way behind at 60 MHz.
>>
>
>Yes, the 274MHz is an extraordinary achievement. It's as measured by the
>ClockSp Basic benchmark, and is therefore some specific instruction mix -
>it's not a timed emulation, it's just running as fast as it can.
>
>Dave has written something about the progression:
>http://stardot.org.uk/forums/viewtopic.php?f=30&t=11328
>
>The simple answer is that the 6502 emulation is written in ARM assembly and
>hand-tuned to the Nth degree by Dominic, with knowledge of the CPU pipeline
>and much reordering of instructions to hide latency. Memory accesses are
>minimised. The 6502's memory is mapped at address zero using the MMU so
>that addressing is simplified.

Interesting, thanks.

I'm not sure if a test like 'ClockSp' is a proper indicator
at these speeds. It may be introducing accuracy problems.
Even if it doesn't, it would be interesting to see the
number of host cycles taken per specific instruction. This
goes for hardware as well as software solutions (and gosh,
how many of them do we have by now ...).

>[...]
>
>The Z80 model, by contrast, is written in C.

Ah, I see.

>[...]


John Kortink