On 08/10/13 17:21, George Gwilt wrote:
Pennel says that (A6,A4) points to the start of data and (A6,A5) points to
immediately past the data area end. This implies that the size of the data
space is A5 - A4.
Yes, A4 is actually the program size, which in my case is 30 bytes only.
It's not a complicated program:
begin bra.s start
dc.l 0
dc.w $4afb
dc.w 8
dc.b 'Test Job'
start moveq #8,d0
moveq #-1,d1
moveq #10,d3
suba.l a1,a1
trap #1
bra.s start
Assembled with GWASL I get a file of 30 bytes and a data space of 4000.
What Marcel (and you) say makes perfect sense. If the job starts at the
address A6 points to, and is 30 bytes long, then the start of the data
space must be A6+30 and as A4 holds the value $1e, that's correct.
I would imagine that A5, on the other hand should hold the address of
A6+30+4000 which would be correct in my case, but I get the extra 12 bytes.
4000 is exactly divisible by 2, 4, 8, 16 or 32 in the powers of two
range. I think QDOSMSQ rounds some memory allocations to the next 8 but
I can't remember if it rounds anything to the next 16.
4030 is divisible by 2.
4042 is divisible by 2, and not much else!
Maybe it's to do with the size of the code file on disc? I changed the
source to add a buffer of 64 words, taking me up to a file size of 158
bytes.
This time, when executed, A4 is $9E (aka 158) which is exactly the size
of the code file, as expected. A5 is 4000+158+12, which is exactly 12
bytes more than the data + code size - and matches up to what I was
already seeing.
In my code size 30 example, I get 42 which is an extra 12 as well.
What's so special about 12 I wonder?
<insert delay while I rummage in the source code>
Right, it must be something in the allocation of memory. I found the
code that creates a job and it simply allocates memory for
#jcb_end+d2+d3 and jcb_end is $68. This is what it requests of the
memory allocation code - so whatever is being allocated must be coming
from that.
I can live with this. It was something unusual that I came across, and I
think it's explained adequately now.
Thanks to all who replied.
Cheers,
Norm.
--
Norman Dunbar
Dunbar IT Consultants Ltd
Registered address:
27a Lidget Hill
Pudsey
West Yorkshire
United Kingdom
LS28 7LG
Company Number: 05132767
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