Re: 14MHz 65816??

[nathan@visi.com (Nathan Mates)]

In article <4v3442$5qm@news.vanderbilt.edu>,
Tilghman Lesher <lesherjt@vuse.vanderbilt.edu> wrote:
>Tony Cianfaglione (tony@ccn.cs.dal.ca) wrote:
>:    I have been in contact with Western Digital regarding their 14 MHz 
>: 65816 chip which they tell me fits onto the accelerator cards such as the 
>: TransWarp GS or Zip GS.  They were not sure if it would replace the stock 
>: GS chip that plugs into the motherboard, which is what I want to do.  I 
>: find the various accelerator cards too buggy to rely on.

>Nope; can't do this.  Remember that the regular 2.8 MHz chip slows down
>to 2.6 MHz because of the 1 MHz bus speed.

   Argh. No. Wrong. The processor internally runs at 2.8Mhz, but due
to ram refresh cycles, the effective speed is about 2.6Mhz. Things are
dropped to 1Mhz under the following conditions: 1) User requests it
(Control panel or via software). 2) "Slow" ram is accessed (banks E0,
E1, which can happen transparently due to shadowing. 3) Softswitches
(//e speaker, 5.25" disk access) are hit, which are just a special
case of 2.

>The accelerators are able to work that fast because they use a type of
>memory called "cache", which quite simply is, fast memory.  The cache
>is "mirrored" back to regular RAM ever so often, so that memory stays
>intact.

   I've already explained this on this thread. Cache is a small (8-32K)
chunk of memory holding recently accessed memory, which can be read at
high speeds. Writes are always done asap, not "every so often."

>If you wanted to use an accelerated chip on the motherboard, you'd have
>to modify the motherboard to speed up the bus, get faster RAM, and hope
>to God that it works (probably won't).

   As I said earlier in this thread, you'd have to redesign the
motherboard from scratch to be able to plug in a faster 65816 and
hope it ran. And the odds of that happening are slim and none.

Nathan Mates

--
<*> Nathan Mates http://www.visi.com/~nathan/      <*>
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