Date   : Tue, 31 Jan 2017 16:29:23 +0000
From   : percy.p.person@... (Ed Spittles)
Subject: Pi-based second processor - fast, flexible,

Indeed, although it's very fast, more testing might say more about exactly
how fast it is.

It's not clear to me that the results do show that we're measuring overhead
- the instruction mixes in each test will differ, so the speedup will
differ. And each additional optimisation will generally affect different
instructions differently. But anyhow, ClockSp is just one possible workload.

Here's my current result, using whichever version I happen to have on the
SDCard, on a Pi Zero connected to a Beeb and therefore running Basic 2:

>CH."clocksp"
BBC BASIC CPU Timing Program
Real REPEAT loop       273.33MHz
Integer REPEAT loop    265.55MHz
Real FOR loop          256.00MHz
Integer FOR loop       254.28MHz
Trig/Log test          299.13MHz
String manipulation    291.00MHz
Procedure call         259.67MHz
GOSUB call             264.70MHz
Combined Average       277.72MHz

Compared to a 2.00MHz BBC B


As a single interesting data point, Dominic said (elsewhere)

The fastest speedup instruction I think is :
Opcode 91 - STA ($00),Y
This I think in 6502 world is 6 cycles and 12 ARM cycle in our world.


As another amusing test, running the pi spigot program, my Pi Zero can
compute 2000 digits of pi in 4.53 seconds. The Beeb at 2MHz takes ...
?still waiting ... 633.5 seconds. So the Pi is emulating at about 279MHz in
that test.

(That's some version of the pi program from
http://stardot.org.uk/forums/viewtopic.php?f=2&t=11458
)

Ed