Helpfile for the BBC A3000 Turbo V1.5
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The BBC A3000 Turbo is a small hardware upgrade
for all Acorn Archimedes BBC A3000 Computers.
It allows under software control to change the
system clock speed from 8 MHz to 12 or 13.33 MHz.
The new system speed depends on the used Crystal.

The software could be controlled from the CLI or
from the WIMP. You can use the following commands:

*Turbo ON 
*Turbo OFF

From the WIMP only click the icon to turn it on or
off. It will go invers when the turbo is off!

The Menu Point "Fix!" is useful for some screen-modes
coz it could happen that the screen wraps some pixels
to the left and "Fix!" will correct it for the desktop!

Other problems could be the RAM-Access-Speed, if you have
a machine with only 1/2MB-120ns RAM then you can clock it
at maximum to 12MHz (80ns) otherwise the Archi won't work!
(It depends on the RAM-Access-Speed which is normally only
120ns, but if you have 4MB-80ns fitted in your Archi then
it works well with 13.33MHz which means an access time of
75ns to the RAM.)  

Because of that the whole system speed is increased
all TIMERS are running ca. 1.5 to 1.67 times faster.
That could give problems with some games, demos or
some module-music-players. Only Digital-Symphony and
some players wich are played over the Vertical-Sync-
IRQ are playing very well. So if some code runs to
fast then turn the turbo off. If you make any ADFS
disc access the turbo is turned off for the access.

Now comes a small table to show the difference
between normal speed and turbo mode!

             A3000 - 8MHz A3000 - 13.33 MHz
H-ROM speed:   200 nS       150 nS
L-ROM speed:   450 nS       300 nS
  RAM speed:   125 nS        75 nS
  ARM speed:  4.85 MIPS    8.07 MIPS
  Data Bus :  25.6 MB/s    42.7 MB/s

PS. the new speed was checked with SI but I have to
change SI a little bit coz it uses mostly the Ticker
clock to calc the speed, but it goes also 1.67 times
faster so I have corrected the calculation routines.

A more impressive example is that you can now work
in MODE 21 or MODE 28. Coz the machine is in these
modes up to 3(!) times faster!!!

If you like this nice upgrade then feel free to send
me somthing from you. (Money, Cars, RiscPC's ... :)

My Addy:
~~~~~~~~
Ingmar Weigel
Gutenbergplatz 54
59821 Arnsberg
United-Germany
Tel.: +49-(0)-2931-13753
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