RAM_SIZE = 65536 # in bytes
max_pixels = 4*RAM_SIZE

print("Expecting use of Nuclaer Tech VGA uPD7220 Graphics Card.")
print(round(RAM_SIZE/1024,2),"K VRAM, up to ",max_pixels," pixels.")

while True:
    min_y_size = 410
    vs_lines = 4
    vbp_lines = 18
    vfp_lines = 10

    max_porch_size = 63


    pixel_time = 1/float(input("Pixel Clock (Mhz) > "))
    signal_time = 2/float(input("Signal Clock (Mhz) > "))

    frame_time = 16683 # 60 Hz
    max_line_time = frame_time/min_y_size

    xres = int(input("Horizontal Resolution > "))
    yres = int(input("Vertical Resolution > "))

    err = False

    if xres/8!=xres//8:
        print("Error:  Horizontal resolution must be a multiple of 8.")
        nval = xres//8
        print("Nearest values are ",8*nval," and ",8*(1+nval))
        err = True
    if xres*yres>max_pixels:
        print("Error: Resolution too high; not enough VRAM to store.")
        print("Try decreasing resolution.  Current usage is ",xres*yres," of ",max_pixels," pixels.")
        err = True
    extra_vblank = max(0,min_y_size-yres-vs_lines-vbp_lines-vfp_lines)
    if(extra_vblank>max_porch_size*2):
        print("Error: vertical resolution MUST be ",min_y_size-vs_lines-2*max_porch_size," pixels or more.")
        print("Increase vertical resolution.")
        err = True
    if(extra_vblank==0):
        # constrained by vertical line count, keep default vertical values
        line_time = frame_time/(vs_lines+vbp_lines+vfp_lines+yres)

        hpixel_time = xres*pixel_time
        if(hpixel_time+5.2>line_time):
            print("Error: not enough time for each line to meet 60Hz.")
            print("Try decreasing resolution or increasng pixel clock frequency.")
            err = True
        
        hsync = round(3.268/signal_time)
        hbp = round(1.6346/signal_time)
        
        extra_line_time = line_time - hpixel_time - signal_time*(hsync+hbp)
        
        hfp = round((.545+extra_line_time)/signal_time)
    else:
        # need to increase vfp to make valid signal

        vfp_lines+=extra_vblank
        
        line_time = frame_time/(vs_lines+vbp_lines+vfp_lines+yres)

        hpixel_time = xres*pixel_time
        if(hpixel_time+5.2>line_time):
            print("Error: not enough time for each line to meet 60Hz.")
            print("Try decreasing resolution or increasng pixel clock frequency.")
            err = True
        
        hsync = round(3.268/signal_time)
        hbp = round(1.6346/signal_time)
        
        extra_line_time = line_time - hpixel_time - signal_time*(hsync+hbp)
        
        hfp = round((.545+extra_line_time)/signal_time)

    if vfp_lines>max_porch_size:
        vbp_lines+=vfp_lines-max_porch_size
        vfp_lines = max_porch_size
    if vbp_lines>max_porch_size:
        vbp_lines = max_porch_size
        # now recalculate hfp
        line_time = frame_time/(vs_lines+vbp_lines+vfp_lines+yres)
        extra_line_time = line_time - hpixel_time - signal_time*(hsync+hbp)
        hfp = round((.545+extra_line_time)/signal_time)
    if hfp>max_porch_size:
        hbp+=hfp-max_porch_size
        hfp = max_porch_size
    if hbp<5:
        hfp-=5-hbp
        hbp = 5
    if hfp<6 and not err:
        print("Error:  could not make horizontal back porch and horizontal front porch big enough!")
        print("Try decrasing the horizontal resolution or increasing either clock speed.")
        err = True
    
    if hbp>max_porch_size:
        print("Error: unable to make video signal meet hardware constraints.")
        print("A higher resolution or lower signal clock speed may be required.")
        err = True
    if(not err):
        print("Horzontal Front Porch: ",hfp)
        print("Horzontal Sync:        ",hsync)
        print("Horzontal Back Porch:  ",hbp)
        print()
        print("Vertical Front Porch: ",vfp_lines)
        print("Vertical Sync:        ",vs_lines)
        print("Vertical Back Porch:  ",vbp_lines)
        line_time = (hfp+hsync+hbp)*signal_time + xres*pixel_time
        vert_time = line_time*(vs_lines+vfp_lines+vbp_lines+yres)
        print()
        print("Expected exact frequency: ",round(1000000/vert_time,2),"Hz")
        print("Image pixel count: ",xres*yres," of maximum ",max_pixels)
        print("Words per line: ",xres//4)
""" # legacy:
if(yres*(xres*pixel_time + .545+3.268+1.6346)+signal_time*vs_lines>frame_time):
    print("Error: not possible.")
else:
    print("Generating timings for "+str(xres)+'x'+str(yres)+' @ 60 Hz')
    
    hextra = (25.422-xres*pixel_time)
    
    hfp = round((.636+hextra)/signal_time)

    print("Horzontal Front Porch: ",hfp)
    print("Horzontal Sync:        ",hsync)
    print("Horzontal Back Porch:  ",hbp)

    
    print("Generating timings for "+str(xres)+'x'+str(yres)+' @ 70 Hz')
    
    hextra = (21.79-xres*pixel_time)
    
    hfp = round((.545+hextra)/signal_time)
    hsync = round(3.268/signal_time)
    hbp = round(1.6346/signal_time)

    print("Horzontal Front Porch: ",hfp)
    print("Horzontal Sync:        ",hsync)
    print("Horzontal Back Porch:  ",hbp)
"""