Re: Real time clock (was Re: C64 Tower)
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Subject:      Re: Real time clock (was Re: C64 Tower)
From:         mmontcha@orednet.org (Matthew Montchalin)
Date:         1998/03/09

Marko Mekel probably wrote:
>> the case in the C64.  The AC frequency is only used for the CIA's Time
>> of Day clock, which isn't used by the KERNAL or BASIC.  Some software
>> uses the CIA's clock, for instance GEOS does.  If you really need the
>> clock, you can build a 555-based oscillator that generates the 50Hz or
>> 60Hz signal.

Lorax was curious:
>Can you give specifics on building this generator and where you
>would need to hook it into the 64?  This bring up another interesting item
>I would love to have for my machines, a real time clock that would keep
>the time after the power is turned off.

Uh, now, wait a second --- it seems that the VIC-II chip /does/ need some
kind of 50 Hz or 60 Hz signal, at the least, and the ROM reset code for a
C-64 makes a guess on that basis, so as to adjust the initialization of
the VIC-II chip to operate properly.  Secondly, doesn't VIC stretch the
clock cycles --- during phi2 or such --- to access screen RAM and color
RAM?  Thus, you really ought to provide SOME kind of oscillation for that
very purpose, if you want to operate your C-64 from a battery (or
equivalent of a non-interruptible power supply).
 
But the most intriguing thing to do, is imagine what a third generation
VIC chip could have been capable of.  Some users want more colors, and
other users want more sprites.  IMO, we ought to look at this from a
hardware angle:  no more of that nonsense about stretching the clock
cycles for letting VIC read RAM to generate an image.  The VIC chip ought
to have had its own private screen RAM and color RAM, and there should
have been a user-selectable toggle to trigger a bank wide DMA to load the
VIC chip from the main C-64 memory!  Also, more sprites would have been
easy to implement if the VIC had had its own 64K of RAM.  And a lesson can
be learnt when comparing my vision of a VIC-III with that miserable 8563
that the C-128 got stuck with:  no more of that bottleneck nonsense.  If
we need to mess with VIC ram, we can do it 1K at a shot.  That way we
could still have screen memory at $0400 and color memory at $d800, then
toggle the DMA to trigger a VIC read, and presto, everything in place.  If
we foolishly wanted to have BASIC do it for us, then that sort of thing
could be wedged into the CHROUT kernal routine.

-- 
At enim vela pendent liminibus grammaticarum scholarum, sed non illa magis
honorem secreti quam tegimentum erroris significant.  -Confessiones St. Aug.

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