[Coco] 6309 microprocessor project - 10-24-2003
gene.heskett at verizon.net
Sat Oct 25 00:44:00 EDT 2003
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.
>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
>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
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
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