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

[Gene Heskett]

On Friday 24 October 2003 22:19, KnudsenMJ at aol.com wrote:
>In a message dated 10/24/03 2:24:27 PM Eastern Daylight Time,
>
>jadonaldson at charter.net writes:
>>    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.
>
>Without dynamic bank switching, the max size application under
> OS9-L2 is 63.5K (taking out the I/O addresses and 256 bytes of
> interrupt vectors and service routines).
>
>Note that system graphics RAM is *not* charged against this 63.5K. 
> Whew!
>
>If the app does its own dynamic bank switching (memory block
> mapping) of 8K blocks, the total program can approach 2 Megs. 
> UltiMusE and Roger Taylor's Projector-3 (I think he has a new name
> for it) do this.

The "myram" automatic formatting ramdisk I wrote also does this.  The 
24 bit offset required to access any byte in a file stored in that 
ramdisk exactly mimics the os9 filesystem by useing it enmass for 
much of the detail work.

>Other OS-supported tricks like pipes and data modules, to coordinate
> an app broken up into multiple processes, can also make apps much
> bigger than 64K. UltiMusE is close to 256K total, and could be lots
> bigger.
>
>The 2 Meg limit has to do with how OS-9 breaks up memory into 8K
> blocks and operates the memory-mapping bits.   It can do at most
> 256 such blocks.  I used to understand the hardware and
> bit-mangling better, but there is a definite limit why OS9 and the
> Coco3 cannot get over 2M without special new system calls. --Mike
> K.

That 256 count of 8192 byte blocks limit uses all 8 available bits in 
the Tony D. method of expanding it to 2 megs.  That kit converts the 
5 bit DAT offset regular os9 l2 used into a full 8 bit one, expanding 
the number of available blocks from 64 to 256.  This all fits within 
the regular os9 l2 framework with a couple of very minor patches.  To 
go any higher would require fairly major surgery to os9 which would 
IMO impact the speed of access noticeably.  There was a time when I 
contemplated it, but with 2 megs, I never came close to using it all 
except while testing myram when its descriptor was set for about 1.7 
megs.

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-- 
Cheers, Gene
AMD K6-III at 500mhz 320M
Athlon1600XP at 1400mhz  512M
99.27% setiathome rank, not too shabby for a WV hillbilly
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Copyright 2003 by Maurice Eugene Heskett, all rights reserved.