[Coco] NitrOS-9 boot module common code

[Gene Heskett]

On Tuesday 11 May 2010, Roger Taylor wrote:
>Here's a snippet from the boot_common.asm file that caught my eye.
>Back2Krn
>	lbsr	HWTerm     call HW termination routine
>	ldx	blockimg,u	pointer to start of os9boot in memory
>	clrb	clear carry
>	ldd	bootsize,u
>
>Doesn't ldd bootsize,u set the CPU Carry?  Is clrb really
>needed?  Heck, every byte counts since the limit is $1D0 bytes.

I don't believe so Roger.  When loading an INT to an INT sized register, 
there can be no condition which would cause a carry.  If that byte is 
valuable, it might be worthwhile to do a one time F$RegDump call to see if 
there are any situations where HWTerm might return with a set carry.  If not, 
save that byte.

>Also, in NitrOS-9 Level Two, can I "request" 512 bytes of space in
>the same manner as the 256-byte stack adjustment or is this pushing
>my luck?  I need to add an optional 512-byte sector mode to my Drive
>Pak modules and just need to find the space so I can use a simple
>deblocking scheme.

AFAIK, you can request as much free memory as the system might have in 
contiguous blocks at that instant.  So 512 bytes basically means you must use 
an int sized register for the pointer into it, byte sized stuff won't work.  
You would probably need another 16 bytes to hold the pointers and such that 
access that 512 byte buffer.  Actually, 2 of them so you can keep reads and 
writes properly segregated.  In any event, I would not do it with a stack 
pointer adjustment, there be sharks in those waters.

-- 
Cheers, Gene
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