[Coco] 6309 microprocessor project - 10-24-2003

[John Collyer]

If you look carefully at the Nocan3 definition below you will see the
complete details of the memory system.  With the NoCan3 memory
extension bits (Bit 6, Bit 5, Bit 4) you can add three more bits to the
already eight bits in the MMU register, which gives you 2^11 different
MMU block numbers.  With the block number * 8192 (Page Size)
you can access 16Megs.  Naturally you have too move the 8K pages
in and out of the microprocessors 64K virtual address space. The
way it stands now OS9 does not recognize more then 2Megs of memory.
The ability to access the 16 Megs is there it is being built into the
emulated
hardware, but it's up to the programmer or the operating system to use it.

When OS9 was made they never knew about the NoCan3 memory extensions.
It does not know there are more then 2Megs available.  The OS9 kernel would
have to be re-written to take advantage of the extra memory available.

; FF9B  Reserved. | 2^11 = 1000000h = 16777216 = 2048 MMU blocks
;                 | for a total memory of 2024 * 8192 = 16,580,608 (16Meg).
;
;       1MB and 2MB bits, Write only.
;       Bit 7 - 16MB Video Bit           NoCan3 bits for 16MB.
;       Bit 6 - 16MB Memory Bit          NoCan3 bits for 16MB.
;       Bit 5 -  8MB Memory Bit          NoCan3 bits for 8MB.
;       Bit 4 -  4MB Memory Bit          NoCan3 bits for 8MB.
;       Bit 3 -  8MB Video Bit           NoCan3 bits for 8MB.
;       Bit 2 -  4MB Video Bit           NoCan3 bits for 8MB.
;       Bit 1 -  2MB Video Bit   Disto & NoCan2/3 bits for 2MB.
;       Bit 0 -  1MB Video Bit   Disto & NoCan2/3 bits for 1MB.

The memory bits (vmmmvvvv) at $FF9B have no effect until a value is sent
to an MMU register, $FFA0-$FFAF. When a value is sent to an MMU register,
the memory bits at $FF9B combine with the MMU register to create a pseudo
11 bit register. This enables access to 2048 (2^11) MMU blocks for a total
memory of 2024 * 8192 = 16,580,608 (16Meg).

----- Original Message ----- 
From: "john donaldson" <jadonaldson at charter.net>
To: <coco at maltedmedia.com>; <coco at maltedmedia.com>
Sent: Friday, October 24, 2003 2:23 PM
Subject: Re: [Coco] 6309 microprocessor project - 10-24-2003


> John,
>    I thought there was a MAX size that a program could be
> under OS9. Are you saying that now we can have a multi
> 100K
> program running at the same time. I always was told that
> 64K was the max size a program could be.
>
> John Donaldson
>