PSG tone period update

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Por hit9918

Prophet (2925)

imagem de hit9918

28-11-2021, 19:32

Below a test program that uses an USR.
It writes the low byte first, and it makes click when going from 255 to 256, but the other direction is no click.

It is clicking only in cases that match the theory that it is a phase reset
The other direction, the error tone is an octave down (and one can nicely hear this tone when in BASIC one adds a = sin(a) for a some more delay)
BUT with an asm update in ~10 microseconds, the error tone is inable to EXIST! it has too long wavelength

10 clear 200,&hbf00

100 restore 9200 : read a : defusr = a : gosub 9000

200 screen ,,0 : sound 8,8 
210 f = 255 : ?"use cursor up/down"
220 defusr1 = f : rem passing the parameter in usr1 0xf3c9
225 x = usr(0)
230 a = stick(0)
240 if a = 1 then f = f + 1
250 if a = 5 then f = f - 1 
260 ?f
300 goto 220


999 end

9000 a$ = ""
9020 if a$="" then read a$

9032 if left$(a$,1)="$"  then a$=mid$(a$,2) : return
9034 if left$(a$,1)="_"  then a$=mid$(a$,2) : goto 9020
9040 if left$(a$,2)="1>" then a$=mid$(a$,3) : l1 = a : goto 9020
9042 if left$(a$,2)="2>" then a$=mid$(a$,3) : l2 = a : goto 9020
9050 if left$(a$,2)="<1" then a$=mid$(a$,3) : b$ = hex$((l1-a-1)AND255) : goto 9110
9052 if left$(a$,2)="<2" then a$=mid$(a$,3) : b$ = hex$((l2-a-1)AND255) : goto 9110

9100 b$=left$(a$,2) : a$=mid$(a$,3)
9110 poke a,val("&h"+b$) : a = a + 1
9120 goto 9020

9200 data &hc000
9210 data 3e00_d3a0_3a9CF3_d3a1__3e01_d3a0_3a9DF3_d3a1__C9$

Por GhostwriterP

Paladin (672)

imagem de GhostwriterP

28-11-2021, 19:36

Alright, tried the later approach and that also seems to work. There is a little less overhead as no comparison with last written value is required.

Por hit9918

Prophet (2925)

imagem de hit9918

28-11-2021, 19:39

GhostwriterP wrote:

so always write 255 to low part then update high part and then update low part?

Wow this is cool Big smile I thought one will have to compare the new value with the register contents. But to write 255 to the low byte does fullfill the requirements "never write a too low value, while a too high value is harmless".

Por GhostwriterP

Paladin (672)

imagem de GhostwriterP

28-11-2021, 19:44

Yes, I think I will adapt this approach for now. Thanks all for sparring with me!

Por Grauw

Ascended (10623)

imagem de Grauw

28-11-2021, 22:41

Thanks to you too, I will keep this simple solution in mind for future projects!

Por Huey

Prophet (2687)

imagem de Huey

29-11-2021, 11:13

Great find guys!

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