Re: MMU prototyping

From: Jim Brain <brain_at_jbrain.com>
Date: Tue, 22 May 2018 18:41:29 -0500
Message-ID: <1be8b1ca-b3e8-0736-ece5-e5463fde3670@jbrain.com>
On 5/22/2018 4:07 PM, Nejat Dilek wrote:
> Nice project!
>
> Does this also use hacks around the PLA like EasyFlash?
I guess it depends on what one defines as a "hack".  This unit simply 
engages the GAME line anytime a memory access that should be outside the 
C64 is requested.  I think that is standard behavior.

>
> Why not use pages of 8 / 16Ks too?
As I looked at the Ultimax map, all pages except for 0-fff and d000-dfff 
were movable.  Doing 8kB means one needs to map in a bank, but can't use 
all of it.  It seemed cleaner to map on 4kB boundaries.  One can handle 
8 or 16kB by simply using 2 or 4 consecutive banks.
>
> I had once a simpler ram extension idea employing the same concept in
> below old project which was published in the Transactor. (But of
> course with a bigger 512K or 1MB sram)
Well, my solution uses a 512kB RAM, and will support up to 256MB.
>
>
>
> It would be nifty to have some external storage mechanism in the cart
> too. It would be really cumbersome to load content into this
> additional ram from the disk drive.
True, and that's a nice thing to consider.  I mainly want to understand 
if anyone sees value in the MMU or the memory before I pursue more work 
(I built the board for other reasons, but decided to implement this 
functionality while I was testing the board asembly).

>
> Regards,
>
> Nejat
>

-- 
Jim Brain
brain@jbrain.com
www.jbrain.com
Received on 2018-05-23 02:00:12

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