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ZX80 development thread

Posted: Thu Dec 07, 2017 10:06 am
by Shaun_B
Hi,

I thought I'd start a thread for ZX80 specific dev talk (it may be an echo chamber) for the ZX80 and compatible clones.

I'll post C, BASIC and Assembly [in C wrapper] snippets here for people to digest, re-use, improve etc...

Thanks,

Shaun.

Re: ZX80 development thread

Posted: Thu Dec 07, 2017 11:01 am
by sirmorris
I think that's a great idea - you may just spark an interest in coding for this challenging machine!

Re: ZX80 development thread

Posted: Thu Dec 07, 2017 11:07 am
by Paul
Yesss,
Wasn't there a wait for keypress for ZX80 in assembly from you somewhere around?
I'm searching for this...
Kind regards Paul

Re: ZX80 development thread

Posted: Thu Dec 07, 2017 11:29 am
by Shaun_B
I'll start with my generic CLS() routine in z88dk (C):

Code: Select all

/**
 * Clears the screen
 *
 * @author	sbebbington
 * @date	22 Aug 2017
 * @version	1.1a
 */
void cls()
{
	__asm
	exx
	ld hl, ($400c)
	ld bc, $0300
	ld d, $21
	inc l
	CLS:
		dec d
		jr z, NEWLINE
		ld (hl), $00
	DECC:
		inc hl
		dec c
		jr z, DECB
		jr CLS
	DECB:
		dec b
		jr z, EXIT
		jr CLS
	NEWLINE:
		ld (hl), $76
		ld d, $21
		jr DECC
	EXIT:
	call $0747
	exx
	__endasm;
}
In usual assembly, you can remove the exx instructions at the start and end of each block (this is required because of the way that C works; preserve the registers before the custom assembly to restore them before returning from the C function wrapper). Calling location $0747 places the cursor at effective position zero of the DFILE (well, position zero must always be a newline, so the next one).

Regards,

Shaun

Re: ZX80 development thread

Posted: Sat Dec 16, 2017 3:43 pm
by nollkolltroll
For cycle-counting madness and getting a stable picture, have a look at my sources to Metropolis :)

Re: ZX80 development thread

Posted: Sat Dec 23, 2017 9:44 pm
by marste
Paul wrote:
Thu Dec 07, 2017 11:07 am
Yesss,
Wasn't there a wait for keypress for ZX80 in assembly from you somewhere around?
I'm searching for this...
Kind regards Paul
Probably not the best part of the code, but if you'll find interesting following is the raw piece of code I used to read keyboard in Z80 flickerfree version of 1K real chess:

Code: Select all


loopkeyread:
    ; DISPLAY SCREEN BLINKING
    push bc
    call display_blinking_cursor
    pop bc

    ld b,$7F ; first time load of keyboard row pointer
    ld hl,tablekeyactions-2
ciclonokeypressed:
    inc hl ;T6x2
    inc hl
    ld a,b ;T4
    in a,($FE) ;T11
    or $e0 ;T7 OR 11100000 (since US based have bit 6 reset, but also different video settings)
    inc a ;T4
    jr nz,keypressed ;T7/12 $FF+1 = 0 = no key pressed
    rrc b ;T8 8 bit rotation to the right
    jr nc,loopkeyreadnokeypressed ;T7/12
    jr ciclonokeypressed ;T12

keypressed:
    ; one key of this row was pressed, process it!
    ld a,c
    or a
    jr nz,loopkeyread ; before another key this one should be left unpressed
    inc c ; flag for debouncing (in reality not repeating, not really debouncing)

-> process action pointed by hl register...
-> ...

;-------------
          djnz_wait1 = 92 ;92
          djnz_wait2 = 40 ;47
      display_blinking_cursor:
          call blinkloop
          ld b,djnz_wait1-djnz_wait2 ;92 ;T 92*13=1196
      wait1: djnz wait1 ;T13
      blinkloop:
          ; invert_char (>>>can be used to loose time between the two calls?)
          ld a,(de)
          xor 128
          ld (de),a
          push de
          out ($FF),a
          ld a,$E8
          ld b,$19   ; B=1 'row' for top border (of C=MARGIN_TOP lines), +24 ($18) rows of 8 lines
          ld c,$38   ; MARGIN_TOP equ $-1
          ld hl,dfile+$8000
          call $01B0
          ld a,$EB
          inc b      ; B=1 'row' for bottom border (of C=MARGIN_BOTTOM lines)
          ld c,$37   ; MARGIN_BOTTOM equ $-1
          ret z      ; delay 5 T-states for good
            ; ... dec c     ; like ld c,$37 since c is still $38 but 1 byte less (and 4 instead of 7 T-States)
            ; ... and (hl)  ; delay 7 T-States (and still 1 bytes) -> 7T+5T almost 4T+7T and 1 byte less
          dec hl     ; why?
          call $01B0
          in a,($FE) ; <<< double if input keyboard...
          ld b,djnz_wait2 ;T 611+576+x
      wait2: djnz wait2 ;T13
          pop de
          ret