[N8VEM: 18366] CP/M alignment

Discussion:

William R Sowerbutts

2014-07-02 13:18:34 UTC

Dear lazyweb,

All the CP/M implementations I have seen have the CCP, BDOS and BIOS aligned
to 256-byte boundaries, ie the low 8 bits of the first address of each are 0.

Does anyone know if this is an actual requirement? Or is it just a common
convention? Perhaps this practice started as a convention and as a result
some applications now make this assumption about BDOS/BIOS entry vector
alignment and will break if this assumption is violated?

Many thanks

Will

_________________________________________________________________________
William R Sowerbutts will-***@public.gmane.org
"Carpe post meridiem" http://sowerbutts.com
main(){char*s=">#=0> ^#X@#@^7=",c=0,m;for(;c<15;c++)for
(m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}

John Coffman

2014-07-02 13:44:12 UTC

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Will, 
 
I would guess that the alignment is a consequence of the original DR
code having been written in pieces without a linker.  That way small
adjustments to the code would not require altering the cross-module
linkage points. 
 
My impression is that there is no alignment requirement in Z80 CP/M
2.2. 
 
--John 
 
 
 
 
On 07/02/2014 06:18 AM, William R Sowerbutts wrote:
<blockquote cite="mid:20140702131834.GA32543-***@public.gmane.org"
type="cite">
<pre wrap="">Dear lazyweb,

All the CP/M implementations I have seen have the CCP, BDOS and BIOS aligned
to 256-byte boundaries, ie the low 8 bits of the first address of each are 0.

Does anyone know if this is an actual requirement? Or is it just a common
convention? Perhaps this practice started as a convention and as a result
some applications now make this assumption about BDOS/BIOS entry vector
alignment and will break if this assumption is violated?

Many thanks

Will

_________________________________________________________________________
William R Sowerbutts <a class="moz-txt-link-abbreviated" href="mailto:will-***@public.gmane.org">will-***@public.gmane.org</a>
"Carpe post meridiem<a class="moz-txt-link-rfc2396E" href="http://sowerbutts.commain(){char*s=">" http://sowerbutts.com
main(){char*s="</a>>#=0> ^#X@#@^7=",c=0,m;for(;c<15;c++)for
(m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}

</pre>
</blockquote>
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Wayne Warthen

2014-07-03 18:09:14 UTC

Permalink

I have not seen any "code level" reason that CCP, BDPS, or CBIOS need to be
page aligned. MOVCPM would not work -- it can be modified to work for page
boundaries, but nothing less than that. Not sure MOVCPM is relevant to
you. There are definitely applications out there that assume page
boundaries.

--Wayne

Will,
I would guess that the alignment is a consequence of the original DR code
having been written in pieces without a linker. That way small adjustments
to the code would not require altering the cross-module linkage points.
My impression is that there is no alignment requirement in Z80 CP/M 2.2.
--John
Dear lazyweb,
All the CP/M implementations I have seen have the CCP, BDOS and BIOS aligned
to 256-byte boundaries, ie the low 8 bits of the first address of each are 0.
Does anyone know if this is an actual requirement? Or is it just a common
convention? Perhaps this practice started as a convention and as a result
some applications now make this assumption about BDOS/BIOS entry vector
alignment and will break if this assumption is violated?
Many thanks
Will
_________________________________________________________________________
"Carpe post meridiem" http://sowerbutts.com
(m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}

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William R Sowerbutts

2014-07-03 23:35:28 UTC

Permalink

There are definitely applications out there that assume page boundaries.

Thanks; this is just what I was worried about. Do you have an example of
one?

W

_________________________________________________________________________
William R Sowerbutts will-***@public.gmane.org
"Carpe post meridiem" http://sowerbutts.com
main(){char*s=">#=0> ^#X@#@^7=",c=0,m;for(;c<15;c++)for
(m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}

Wayne Warthen

2014-07-05 05:48:25 UTC

Permalink

I'm afraid I don't remember any examples offhand, but quite sure I encountered it.

Wayne

William R Sowerbutts

2014-07-06 17:55:13 UTC

Permalink

I didn't have to look far -- both SURVEY.COM and CLRDIR.COM on the RomWBW ROM
disk image require the BIOS to be page aligned.

Will

Post by Wayne Warthen
I'm afraid I don't remember any examples offhand, but quite sure I encountered it.
Wayne
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_________________________________________________________________________
William R Sowerbutts will-***@public.gmane.org
"Carpe post meridiem" http://sowerbutts.com
main(){char*s=">#=0> ^#X@#@^7=",c=0,m;for(;c<15;c++)for
(m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}