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2011-12-30 12:14

Flavioweb

Registered: Nov 2011
Posts: 463

assembly sin gen code request

i need a code (assembly) to gen sin table. I need to set start, end and step value. Someone could help?

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2012-01-18 08:57

Graham
Account closed

Registered: Dec 2002
Posts: 990

Quoting Cruzer

I'm also usually using Graham's mirror trick in bigger productions, even with only a 64 byte table. :)

Yes, if you add an offset of 0.5 to the sinus index (0.5 to 255.5 instead of 0 to 255), you can use a 64 byte table. This works nice for plasmas, sinus movements etc. However for "real maths" like 3D rotation or similar, it's better to use a sinus wave without that 0.5 index.

2012-01-18 20:54

Wisdom

Registered: Dec 2001
Posts: 90

Quoting ChristopherJam

Of course, it's possible a delta compression scheme might end up winning out over a calculation.. and any entry of more than 256 bytes of code is pretty much an automatic fail!

In Tied, there is a simple delta encoded sinus table, consisting of only 8 bytes, but the decoder itself is around 38 bytes (might change due to initialization in a different perspective). Extends a full sinus for 00-3F values to a 256 bytes table.

There is also a second one, which has a more complex shape, consisting of a 32 bytes table and a separate 40 bytes decoder (again, might be different a byte or two in a different initialization scenario). Again, extends to a 256 bytes table with values between 00-3F.

2012-01-19 12:45

Adam

Registered: Jul 2009
Posts: 323

Quoting SIDwave

... what i want to say really, is, why dont someone make a c64 tool ? if its so important, then make a c64 generator? :)

Hi Jan, Here is a tool that will allow you to generate sine waves using MS-Windows:

Sinus Creator V3 by 'The Gang'
http://www.thegang.nu/get_data.php?type=attachment&id=160

The website says version 2.x but the program in the zip archive is version 3. This program is very useful ;)
Output: Binary, Assembler, BASIC, C, C Source and WAV Audio samples =D

2012-01-19 13:43

ChristopherJam

Registered: Aug 2004
Posts: 1409

This routine has an accuracy ±3 (should be able to improve that by tweaking the table a little), but relies on interrupts being clear, character DMA disabled, and voice 3 of SID being fully decayed with a release rate of zero! 58 bytes including table, piecewise linear using env3 to select one of 13 segments:

sin=$4000
v3ctrl = $d40e+4
v3AD   = $d40e+5
v3SR   = $d40e+6
env3   = $d41c

initSin
	ldx#$50
	stx v3AD
	inc v3ctrl
	lda#127
	clc
lp 
ly  ldy#63
  	eor#$ff
	sta sin-$50,x
	sta sin+64,y
	eor#$ff
	sta sin+128-$50,x
	sta sin+192,y           ;26 cycles

	rol  ; note this will clear carry
	ldy env3  ; increases by 1 every 208 cycles for attack=5,
	sbc dt,y
  	lsr
	inx
	dec ly+1
  	bpl lp            ; 22+26 =48 for entire loop

	rts
dt
	.byt 5,5,5,5,5, 4,4,3,3,2, 2,1,0,255

CIA would probably be a better bet than SID, but I'm not very familiar with it, and it's less of an evil hack :)

2012-01-19 19:10

Cruzer

Registered: Dec 2001
Posts: 1048

Generating sines with the SID, now that's what I call a hack! Is it based on sine-like waveforms, or is the SID just used as a counter as the comments imply?

2012-01-19 19:27

chatGPZ

Registered: Dec 2001
Posts: 11386

the envelope generator uses some sort of spline approximation, so its linear steps and the slope changes at a few points.

2012-01-19 20:38

ChristopherJam

Registered: Aug 2004
Posts: 1409

Much simpler than all that; I just needed a value that increased by one every four or five iterations through the loop. The sin table generated is a linear approximation calculated in 8.1 fixed point, with a new slope value for each envelope increment.

Envelope generation is itself piecewise linear in the decay and release phases, but attack (as used here) just increases at a constant rate.

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