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41-CL Routine of the week: MMUSWAP
Posted by Ángel Martin on 4 Nov 2012, 5:57 a.m.
Often I get in a situation with my CL setup where I need to exchange the location of two pages; the virtual equivalent to swapping two 4k-modules plugged in the "normal" 41 machine ports.
The short routine below is a practical solution using a couple of functions from the AMC_OS/X (can be replaced with the same functions in the CDD or standard OS/X Modules).
It works by exchanging the MMU mappings to the page pointers, as simple as that: no need to type the ROM ID's, or do any data copying - such is the power of the MMU design.
Simply enter the FROM:/TO: page numbers in Y and X respectively (in decimal), then execute MMUSWP and the job is done.
Valid inputs are 8 to 15. The CL will prevent you from re-mapping the OS, but stay clear form 0-5 in the inputs to avoid getting in trouble. Better yet, modify the program to prevent any accidental invalid page range.
Page 4 is definitely to be excluded. It's up to you to allow 6 and 7 as well, just remember the OS rules about the printer and HPIL pages.
See the code below, short and sweet as promised:
01 LBL "MMUSWP" 02 8 03 WSIZE 04 RDN 05 XEQ 00 06 ASTO T 07 XEQ 00 08 ASTO L 09 XEQ 02 10 R^ 11 STO L 12 RDN 13 LBL 02 14 "804" 15 ARCLH 16 "|-0" 17 ARCL L 18 YPOKE 19 X<>Y 20 RTN 21 LBL 00 22 "804" 23 ARCLH 24 "|-0-1111" 25 YPEEK 26 ASHF 27 X<>Y 28 END
Note: first byte in lines 16 and 24 is the APPEND character, "|-"
First off, this is for single pages and not for complete modules. Using it on multiple-page modules will of course create havoc with their FATs and general arrangements.
Second, if including the AMC_OS/X itself in the swapping it should be in the FROM: location (Y register). Otherwise it’ll get unmapped before the program ends, and won’t be possible to use the remaining ARCLH instruction.
For the same reason swapping the page mapped to the YFNS will be a problem if it's first un-mapped, as the following YPOKE instruction will NOT be found by the OS. Moreover, even using it in the FROM: location won't suffice: the last YPOKE line will be found but it'll then attempt to "re-map YFNS from itself", which will freeze the calculator just the same. In summary, do NOT attempt to swap the YFNS page at all.
Better safe than sorry: insert this subroutine before line 21:
23 *LBL 01 24 "OS AREA" 25 6 can use 7/8 to protect 26 X>Y? the HPIL and PRINTER 27 PROMPT 28 X>Y? 29 GTEND go to .END. 30 RDN 31 "PG=YFNS" 32 YFNZ? 33 X=Y? 34 PROMPT 35 X=Y? 36 GTEND go to .END. 37 RDN 38 X<>Y swap FROM:/TO: 39 RTN
And insert these two lines before line 01 to "anchor" YFNS to its current page:-
01 XEQ 01
02 XEQ 01
Edited: 4 Nov 2012, 2:55 p.m.
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