Talbot Fantasy 7
by Deater (Vince Weaver)
vince@deater.net
http://www.deater.net/weave/vmwprod/tfv/
Background
~~~~~~~~~~
What you've always wanted, a poorly done FF7 clone for the Apple II.
Yes, I'm using the 40x40 15-color Low-resolution graphics mode of
the Apple II. This means the game could in theory run on the original
Apple II released in 1977 (if you had been fabulously rich enough to
populate all 48k of RAM).
Memory Map
~~~~~~~~~~
$00 zero page
$01 stack
$02-$03 ??
$04-$07 lores page 1
$08-$0b lores page 2
$0c-$0f background graphics
$10-$1f ??
$20-??? code AE-20 = 36.4k
$AE-$B5 music buffer 2k
$B6-$BD multiply tables 2k
$BE-$BF ??
$C0-$CF I/O
$D0-$FF ROM
Mode7 Optimization Notes
~~~~~~~~~~~~~~~~~~~~~~~~
Original implementation:
Multiplying 1.0 * 2.0 = 2.0, took 707 cycles
Multiplying ff.ff * ff.ff = 0.0, took 761 cycles
Cycles: flying= 162
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 88,179
Cycles: mode7= 76,077
Cycles: lookup_map= 33,920
Cycles: put_sprite= 2,561
==================================
Total = 200,971
Frame Rate = 4.98 fps
Update Multiply to use zero page addresses:
Multiplying 1.0 * 2.0 = 2.0, took 616 cycles
Multiplying ff.ff * ff.ff = 0.0, took 664 cycles
Cycles: flying= 162
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 76,561
Cycles: mode7= 76,077
Cycles: lookup_map= 33,920
Cycles: put_sprite= 2,561
===================================
Total = 189,353
Frame Rate = 5.28 fps
Update to use "fast multiply" w 2kB squares table lookup:
Multiplying 1.0 * 2.0 = 2.0, took 228 cycles
Multiplying ff.ff * ff.ff = 0.0, took 272 cycles
Cycles: flying= 162
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 27,041
Cycles: mode7= 76,077
Cycles: lookup_map= 33,920
Cycles: put_sprite= 2,561
=================================
Total = 139,833
Frame Rate = 7.15 fps
Update to optimize fast multiply (reusing NUM1H, return results in register)
Multiplying 1.0 * 2.0 = 2.0, took 234 cycles
Multiplying ff.ff * ff.ff = 0.0, took 278 cycles
Cycles: flying= 162
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 24,935
Cycles: mode7= 73,925
Cycles: lookup_map= 33,920
Cycles: put_sprite= 2,561
=================================
Total = 135,575
Frame Rate = 7.38 fps
Add a cache to lookup_map
Cycles: flying= 162
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 24,935
Cycles: mode7= 73,445
Cycles: lookup_map= 24,649
Cycles: put_sprite= 2,561
=================================
Total = 125,824
Frame Rate = 7.95 fps
Don't draw sky every frame
Cycles: flying= 162
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 24,935
Cycles: mode7= 69,099
Cycles: lookup_map= 24,649
Cycles: put_sprite= 2,561
=================================
Total = 121,478
Frame Rate = 8.23 fps
Move checking if over water out of critical section
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 24,935
Cycles: mode7= 54,374
Cycles: lookup_map= 24,712
Cycles: put_sprite= 2,561
=================================
Total = 106,841
Frame Rate = 9.36 fps
Move to 40x40 mode
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 49,613
Cycles: mode7= 123,701
Cycles: lookup_map= 48,847
Cycles: put_sprite= 2,561
=================================
Total = 224,981
Frame Rate = 4.44 fps
Remove some unnecessary zero page copies in the mode7 code
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 49,613
Cycles: mode7= 141,269
Cycles: lookup_map= 21,718
Cycles: put_sprite= 2,561
================================
Total = 215,420
Frame Rate = 4.64 fps
A few more minor cleanups in the Y loop
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 49,613
Cycles: mode7= 140,858
Cycles: lookup_map= 21,718
Cycles: put_sprite= 2,561
===============================
Total = 215,009
Frame Rate = 4.65 fps
Add some self-modifying code to inner loop:
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 49,613
Cycles: mode7= 131,610
Cycles: lookup_map= 21,718
Cycles: put_sprite= 2,561
================================
Total = 205,761
Frame Rate = 4.86 fps
More self-modifying code, also move SCREEN_X to X register
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 49,613
Cycles: mode7= 118,034
Cycles: lookup_map= 22,747
Cycles: put_sprite= 2,561
================================
Total = 193,214
Frame Rate = 5.18 fps
Remove unneeded precision in the 8.8 x 8.8 fixed point multiply
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 43,588
Cycles: mode7= 118,034
Cycles: lookup_map= 22,747
Cycles: put_sprite= 2,561
================================
Total = 187,189
Frame Rate = 5.34 fps
In-line unsigned multiply inside of signed multiply (save 12 cycles)
Multiplying 1.0 * 2.0 = 2.0, took 198 cycles
Multiplying ff.ff * ff.ff = 0.0, took 218 cycles
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 40,888
Cycles: mode7= 118,034
Cycles: lookup_map= 22,747
Cycles: put_sprite= 2,561
================================
Total = 184,489
Frame Rate = 5.42 fps
Have loop counter count down from 40 instead of count up (avoid compare)
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 40,888
Cycles: mode7= 115,538
Cycles: lookup_map= 22,747
Cycles: put_sprite= 2,561
================================
Total = 181,993
Frame Rate = 5.49 fps
Move spacez updates out of line and also do some self modifying code
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 40,680
Cycles: mode7= 114,830
Cycles: lookup_map= 22,747
Cycles: put_sprite= 2,561
================================
Total = 181,077
Frame Rate = 5.52 fps
Re-arranged multiply result register to allow more optimization.
This looks like a pessimization, but it's because the cycle counting code
had been undercounting and missed a few add routines :(
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 40,680
Cycles: mode7= 115,150
Cycles: lookup_map= 22,747
Cycles: put_sprite= 2,561
================================
Total = 181,397
Frame Rate = 5.51 fps
Make lookup_map inline. Again it looks like an impressive speedup
but some of this was fixing the cycle count estimates.
Cycles: flying= 187
Cycles: getkey= 46
Cycles: page_flip= 26
Cycles: multiply= 40,680
Cycles: mode7= 111,882
Cycles: lookup_map= 19,872
Cycles: put_sprite= 2,561
================================
Total = 175,254
Frame Rate = 5.71 fps
Each cycle removed from inner X loop saves
32*40=1280 cycles
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