8 Sep
2016
8 Sep
'16
5:07 p.m.
From: Kyle Owen: Thursday, September 08, 2016 3:53 PM
How does the following compare to your BSWEMU, by the
way? This ensures
that the link bit remains untouched, which may or may not be important in
every case of BSW in my application.
I'm sure I've seen some code before that does
this, but I can't seem to
find any now that I'm looking for it. Maybe there's a shorter way. I think
this takes 23 words if you include the (0100), (7700), and (0077), which
may or may not also be used elsewhere in the first page where I put this
subroutine.
Here's my slightly optimized version, for what it's worth:
1 *400
2 /
3 / BSW emulation
4 /
5 00400 0000 bsw, .-.
6 00401 3216 dca saveac / Save AC
7 00402 7630 szl cla / Link set?
8 00403 7140 cll cma / Yes, remember it
9 00404 3217 dca savel
10 00405 1216 tad saveac / Get 0 xxx xxx yyy yyy
11 00406 0220 and c7700
12 00407 1216 tad saveac / x xx xxx0 yyy yyy
13 00410 7006 rtl
14 00411 7006 rtl
15 00412 7006 rtl / 0 yyy yyy xxx xxx
16 00413 2217 isz savel / Was link set?
17 00414 7020 cml / Yes, restore it
18 00415 5600 jmp i bsw / return
19 00416 0000 saveac, .-.
20 00417 0000 savel, .-.
21 00420 7700 c7700, 7700
22 $
There is a fair chance that each of saveac, savel, and c7700 can be reused
elsewhere.
Some assemblers flag the "(" construct when used on page 0, BTW. It's more
correct
to use "[" there (or to avoid both).
I'm a "family of 8" guy, so I avoid using BSW to begin with.
Vince