Z80 speed detect?

[MIRKOSOFT]

Hi!

I ever wanted to get speed of 8502CPU speed, SuperCPU speed... it's done, no problem...

...but C128 has also Zilog Z80 processor for CP/M mode.

So, here's Q: Is possible to detect speed of Z80 (MHz) also in standard C128 mode?

'Cause I'm not sure if is Z80 turned off if CP/M mode is inactive....

Many thanks for help.

Miro

[Hydrophilic]

The Z80 runs at a fixed, effective speed of 2MHz, IF it is running at all.  Normally only one processor (the 8502 or Z80) is running.  I have read somewhere that you can run both at the same time, but then you have to find a sequence of bytes that decodes to valid instructions for both processors... a very difficult and impractical task.

[XmikeX]

I believe you're thinking of the Mäkelä USENET thread from 1997.
One copy (at comp.sys.amstrad.8bit) is seen here -

http://groups.google.com/group/comp.sys.amstrad.8bit/browse_thread/thread/df83ad39c6a61b4c/81fb88cd5a3479cf?q=z80+8502+bus+makela#81fb88cd5a3479cf

snippet follows :

From Marko Mäkelä -      
Some years ago I played with the Commodore 128's MMU and noticed that
when you activate the Z80 mode and the C64 mode simultaneously, both
processors (8502 and Z80) will be activated at the same time.  Of
course this will normally cause a crash, because neither processor can
fetch meaningful instructions.  I assume that the address and data
busses will be ANDed together, and also the R/-W signal of the 8502
will be ANDed with the -WR signal of the Z80. 

Years later, I'm still waiting for a follow-up and confirmation.
Anyone here with skills, analyzer, scope, motivation, and too much free time? 

XmX