[sdcc-devel] [ sdcc-Feature Requests-1017497 ] 256 byte arrays into paged area?

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Feature Requests item #1017497, was opened at 2004-08-27 12:37
Message generated for change (Comment added) made by maartenbrock
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=350599&aid=1017497&group_id=599

Category: None
Group: None
Status: Open
Priority: 1
Submitted By: Frieder Ferlemann (frief)
Assigned to: Nobody/Anonymous (nobody)
Summary: 256 byte arrays into paged area?

Initial Comment:
Hi,

it would be nice if char arrays of 256 byte length were
automagically allocated 
to a paged (256 byte aligned) area:

.area XBSEG    (XDATA,PAG)

This might allow to reduce the overhead for an xdata
array access
xdata unsigned char buf[256];

From:

; buf[ head ] = c;
;     genPlus
        mov     a,_head
        add     a,#_buf
        mov     dpl,a
        clr     a
        addc    a,#(_buf >> 8)
        mov     dph,a
        mov     a,r2
        movx    @dptr,a

Down to:

; buf[ head ] = c;
;     genPlus
;     genPlus aligned array
        mov     dpl,_head
        mov     dph,#(_buf >> 8)
        mov     a,r2
        movx    @dptr,a

(SDCC generates this code if an absolute address like
"at 0x8000" was 
specified for the array. This request is somewhat
similar to RFE #774501 
but it doesn't require an additional keyword)


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>Comment By: Maarten Brock (maartenbrock)
Date: 2004-11-29 17:23

Message:
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Looked into this. It's probably not so hard to make the linker 
move such arrays to the front of the list and thereby 
allocating them to page boundaries. This assumes xdata 
starts at a page boundary. (Not true if pdata is used and 
<256 and no xstack. Also not true if --xram-loc says so.)

But the problem is that the compiler doesn't know all this. So 
a special keyword might be in place. Maybe something like "at 
page" instead of "at 0x0000"?

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Comment By: Frieder Ferlemann (frief)
Date: 2004-10-19 18:36

Message:
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user_id=589052

Hi Maarten,
thanks a lot for adding pdata access!) !) 

When I filed this request, I had buffers (like those two 
256 byte buffers in sdcc/device/lib/serial.c) in my mind.
I wouldn't want to loose the newly won memory space 
for only one of those buffers;) 


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Comment By: Maarten Brock (maartenbrock)
Date: 2004-10-19 14:02

Message:
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user_id=888171

Feel free to store it in pdata instead of xdata

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=350599&aid=1017497&group_id=599