Re: [stella] programming teaser

Subject: Re: [stella] programming teaser
From: "Fred Quimby" <c9r@xxxxxxxxxxx>
Date: Fri, 20 May 2005 17:45:04 -0400
What bankswitching scheme are you using?  I ask because I'm not aware of any 
that allow multiple banks of RAM except for E7 or Starpath, and the Kroko 
cart doesn't support these.

>The whole point being that in a kernel you don't necessarily need to 
>a counter value, nor branch when it reaches the final value.  In notBD,
>there are n rows, each done by identical code in consecutive banks.  By
>switching banks, the code keeps running, but the last bank has a "rts" just
>after the switch.  It's an interesting technique, used in notBD's new 
>(worked on by Thomas and I) -- and without which, the kernel probably
>wouldn't be possible.
>In answer to Dennis, this particular code runs in BOTH RAM and ROM.  It's a
>bit weird, but the code is defined in ROM, and you (can) call the ROM
>routine still.  But it is also copied to multiple RAM banks, and the first
>bankswitch will switch to the code running in RAM (because, in the
>bankswitch scheme I am using, there is only one switchable bank -- in an
>address area shared by both the ROM-switchable and RAM-switchable banks).
>Another way to achieve the same effect as the rather unique 'tricky'
>subroutine would be with self-modifying code, but it costs cycles.  The
>above technique is totally cycle-free in terms of detecting and forcing the
>end of a loop.  You do, of course, need the right memory architecture to
>achieve this :)
>----- Original Message -----
>From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
>To: <stella@xxxxxxxxxxxxxxxxxx>
>Sent: Friday, May 20, 2005 9:07 PM
>Subject: Re: [stella] programming teaser
>Fred wrote:
> > Maybe your bankswitching instruction swaps the code out after x=8 and
> > finds
> > an RTS where the ldy #21 was?
>BTW: THAT one was solely Andrew's idea! ;-)
>Have fun!
>Thomas Jentzsch | *** Every bit is sacred ! ***
>tjentzsch at web dot de |
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