Re: Bar counts and repeats in repetitive music

[Peter Toye]

David,

Z80 - far too modern for me. I was using machine code in the 1960s!

Best regards,

Peter
mailto:address@hidden
www.ptoye.com

-------------------------
Tuesday, February 28, 2017, 8:18:55 PM, you wrote:

> Peter Toye <address@hidden> writes:

>> David and other,

>> All of which makes me think that it's not really worth while pursuing
>> this development any further. As an ex-programmer (yes, I sometimes
>> did write comments, but in assembler you rather have to)

> How else would you keep track of cycle counts?

>         .Z80

>         NAME    ('SCROLL')

>         ENTRY   SCRLFT,SCRRIG
>         PUBLIC  SCRX

>         EXT     STAGE,SHBTAB
>         EXT     DELAY
>         EXT     SCREEN,OUTCTL

>         DSEG

> SCRLFT: LD      IY,STAGE        ;14(20)
>         LD      HL,SCRX         ;30
>         LD      A,4             ;37
>         ADD     A,(HL)          ;44
>         LD      (HL),A          ;51
>         ADD     A,44            ;58
>         LD      L,A             ;62
>         LD      H,0             ;69
>         LD      E,L             ;73
>         LD      D,H             ;77
>         ADD     HL,HL           ;88
>         ADD     HL,DE           ;99
>         EX      DE,HL           ;103
>         ADD     IY,DE           ;118
>         LD      A,12            ;125
>         LD      (SPSAVE),SP     ;145
>         LD      SP,SCREEN+22    ;155
> SCRL05: EX      AF,AF'          ;4
>         LD      A,(IY)          ;23
>         AND     31              ;30
>         ADD     A,A             ;34
>         LD      C,A             ;38
>         LD      B,0             ;45
>         LD      HL,SHBTAB       ;55
>         ADD     HL,BC           ;66
>         LD      E,(HL)          ;73
>         INC     HL              ;79
>         LD      D,(HL)          ;86
>         LD      C,4             ;93
> SCRL10: LD      A,70H           ;7
>         OR      C               ;11
>         DEFW    OUTCTL  ;22
>         LD      B,16            ;29
> SCRL11: EX      DE,HL           ;4
>         LD      E,(HL)          ;11
>         INC     HL              ;17
>         LD      D,(HL)          ;24
>         INC     HL              ;30
>         EX      DE,HL           ;34
>         REPT    11
>         EX      (SP),HL         ;35
>         DEC     SP              ;41
>         DEC     SP              ;47
>         ENDM                    ;551
>         EX      (SP),HL         ;586
>         LD      HL,22+40H       ;596
>         ADD     HL,SP           ;607
>         LD      SP,HL           ;611
>         DJNZ    SCRL11          ;10008
>         SRL     C               ;10016
>         JR      C,SCRL20        ;10023 / 30237
>         LD      HL,-16*40H      ;10033
>         ADD     HL,SP           ;10044
>         LD      SP,HL           ;10048
>         JP      SCRL10          ;10058
> SCRL20: LD      A,70H
>         DEFW    OUTCTL
>         EX      AF,AF'          ;30241
>         DEC     A               ;30245
>         INC     IY              ;30255
>         JP      NZ,SCRL05       ;363335
> SCRL21: LD      SP,(SPSAVE)     ;363373
>         LD      A,182
>         JP      DELAY

> Though I have to admit that this was from my youth, an age where you
> consider yourself and your memory immortal.

> DELAY is sort of a misnomer: it does not actually do any delay but
> tells the timing logic how much time a routine spent doing its job.
> Since we are talking about 363373 cycles on a 4MHz machine, the unit for
> "DELAY" would appear to be slices of 0.5ms.

> Scrolling by 16 pixels on a bitmapped display by using

>         EX      (SP),HL         ;19
>         DEC     SP              ;25
>         DEC     SP              ;31

> as the workhorse rather than

>         LDI ;16
>         LDI ;32

> may seem a bit overoptimizing but it leaves quite more registers
> available for loop control and stride adjustment and only takes 3 bytes
> instead of 4.

> Sorry for the distraction: your remark about the necessity of commenting
> assembly language triggered this memory.

> It turns out that basically the module moving player and monsters
> actually has bonafide comments in it (and it is not timing-critical so
> there are no cycle counts and no call of DELAY).  A collaborator
> insisted on them.