Debugging

[boriel]

Hi, Britlion

Sorry for the delay! (as always)
Are you using this FastPlot implementation?
https://zxbasic.readthedocs.io/en/docs/l.../fastplot/

Ok. You're using the 2nd implementation (the Wiki one does not include the lookup table?)

Update: In the original code, even with PAUSE 0, the code plotted in the wrong region of the screen for me...
Update: I've fastcalled your routine. Now it does not hang, but still the plots are a bit odd

Code:

SUB Fastcall FastPlot (x as uByte, y as uByte)

    ASM
    pop hl ; hl = RETURN ADDRESS
    ex (sp), hl ; Callee H = y
    ex de, hl   ; d = y

    ld HL,FastPlotYValue+1
    ld (hl), d

    FastPlotASMStart:
        ld      hl,BLtabpow2
        ld      (FastPlotSaveX+1),A
        and     7       ; x mod 8
        add a,l
        ld l,a
        jr nc, FastPlotSkip1
        inc h

    FastPlotSkip1:
        ld      e,(hl)     ; e contains one bit set
        ld      hl,BLTabLinIdx

    FastPlotYValue:
        ld      a,0 ; Self modding code that puts y value here
        add a,l
        ld l,a
        jr nc, FastPlotSkip2
        inc h

    FastPlotSkip2:
        ld      a,(hl)      ; table lookup
        ; OR a      <= CLEAR CARRY FLAG missing??

        rrca
        rrca
        rrca
        ld h,a
        and %11100000
        xor h
        or %01000000
        ld h,a   ;- this is faster at 35 T states to do hl=a*32

    FastPlotSaveX:
        ld      a, 255 ; X Self Modifying - this is written into to save X earlier.
        rrca
        rrca
        rrca
        and %00011111        ;x / 8 19 T states
      
        or      l
        ld      l,a         ; + x/8.

        ld      a,(hl)
        or      e           ; or = superposition mode.
        ld      (hl),a      ; set the pixel.

    END ASM
    return

    #ifndef BLTabLineIdxPresent
    #define BLTabLineIdxPresent
    ASM
        ;; small screen lines lookup table

    BLTabLinIdx:
        defb    0,8,16,24,32,40,48,56,1,9,17,25,33,41,49,57
        defb    2,10,18,26,34,42,50,58,3,11,19,27,35,43,51,59
        defb    4,12,20,28,36,44,52,60,5,13,21,29,37,45,53,61
        defb    6,14,22,30,38,46,54,62,7,15,23,31,39,47,55,63

        defb    64,72,80,88,96,104,112,120,65,73,81,89,97,105,113,121
        defb    66,74,82,90,98,106,114,122,67,75,83,91,99,107,115,123
        defb    68,76,84,92,100,108,116,124,69,77,85,93,101,109,117,125
        defb    70,78,86,94,102,110,118,126,71,79,87,95,103,111,119,127

        defb    128,136,144,152,160,168,176,184,129,137,145,153,161,169,177,185
        defb    130,138,146,154,162,170,178,186,131,139,147,155,163,171,179,187
        defb    132,140,148,156,164,172,180,188,133,141,149,157,165,173,181,189
        defb    134,142,150,158,166,174,182,190,135,143,151,159,167,175,183,191

    BLtabpow2:
        ;; lookup table with powers of 2
        defb    128,64,32,16,8,4,2,1  

    END ASM
    #endif  
          
END SUB

FOR n=40 to 50                                                                  
FastPlot (n,60)
next n

FOR n=40 to 50                                                                  
FastPlot (n,50)
pause 0
next n